Refresh of the observer pattern content

[adegeo]

Summary

I had most of this done last week and I just needed some fit-and-finish work today, but then I noticed that AI had really gone of the rails with the code migration. It migrated the code but had also rewritten it, desynching it with the article. The rewrite was good, but it hadn't accounted for the fact that the code project was used by two different articles. In the effort to simplify and rewrite, it had ruined the other article's content.

I had to rewind, and fix all of that.

It's now in a good place.

Fixes #52697

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Internal previews

📄 File	🔗 Preview link
docs/standard/events/how-to-implement-a-provider.md	How to implement a provider
docs/standard/events/how-to-implement-an-observer.md	"How to implement an Observer"
docs/standard/events/observer-design-pattern-best-practices.md	Best practices for the observer design pattern
docs/standard/events/observer-design-pattern.md	docs/standard/events/observer-design-pattern

[Copilot]

Pull request overview

This pull request refreshes the Observer design pattern documentation by modernizing the articles and migrating the associated code samples into the docs-local snippets/ structure (including updated .NET target frameworks), while removing legacy snippet projects under samples/snippets/... that are no longer referenced.

Changes:

• Update Observer pattern articles (including best practices and provider/observer how-tos) with refreshed guidance and updated snippet references.
• Migrate the temperature monitor and baggage claim samples to docs/standard/events/snippets/..., adding new C# and Visual Basic snippet projects targeting net10.0.
• Restructure the observables samples into language-specific folders and remove legacy shared C# files and older samples/snippets/... sources.

Reviewed changes

Copilot reviewed 42 out of 43 changed files in this pull request and generated 4 comments.

Show a summary per file

File	Description
samples/snippets/visualbasic/VS_Snippets_CLR/conceptual.observerdesignpattern/vb/provider.vb	Remove legacy VB baggage provider implementation (no longer referenced).
samples/snippets/visualbasic/VS_Snippets_CLR/conceptual.observerdesignpattern/vb/observer.vb	Remove legacy VB arrivals monitor implementation (no longer referenced).
samples/snippets/visualbasic/VS_Snippets_CLR/conceptual.observerdesignpattern/vb/module1.vb	Remove legacy VB program entry point (no longer referenced).
samples/snippets/visualbasic/VS_Snippets_CLR/conceptual.observerdesignpattern/vb/baggageinfo.vbproj	Remove legacy VB project file for baggage sample.
samples/snippets/visualbasic/VS_Snippets_CLR/conceptual.observerdesign.howto/vb/temperaturemonitorvb.vbproj	Remove legacy VB temperature monitor project file.
samples/snippets/visualbasic/VS_Snippets_CLR/conceptual.observerdesign.howto/vb/provider.vb	Remove legacy VB provider implementation for temperature sample.
samples/snippets/visualbasic/VS_Snippets_CLR/conceptual.observerdesign.howto/vb/observer.vb	Remove legacy VB observer implementation for temperature sample.
samples/snippets/visualbasic/VS_Snippets_CLR/conceptual.observerdesign.howto/vb/data.vb	Remove legacy VB temperature data type snippet.
samples/snippets/csharp/VS_Snippets_CLR/conceptual.observerdesign.howto/cs/temperaturemonitorcs.csproj	Remove legacy C# temperature monitor project file.
samples/snippets/csharp/VS_Snippets_CLR/conceptual.observerdesign.howto/cs/provider.cs	Remove legacy C# provider implementation for temperature sample.
samples/snippets/csharp/VS_Snippets_CLR/conceptual.observerdesign.howto/cs/program.cs	Remove legacy C# program entry point for temperature sample.
samples/snippets/csharp/VS_Snippets_CLR/conceptual.observerdesign.howto/cs/observer.cs	Remove legacy C# observer implementation for temperature sample.
samples/snippets/csharp/VS_Snippets_CLR/conceptual.observerdesign.howto/cs/data.cs	Remove legacy C# temperature data type snippet.
docs/standard/events/snippets/shared/how-to-provider-observer/vb/temperaturemonitorvb.vbproj	Add new docs-local VB snippet project targeting net10.0 for the provider/observer how-tos.
docs/standard/events/snippets/shared/how-to-provider-observer/vb/provider.vb	Add refreshed VB provider sample (temperature monitor) with snippet markers.
docs/standard/events/snippets/shared/how-to-provider-observer/vb/program.vb	Update VB program to run the async temperature sample.
docs/standard/events/snippets/shared/how-to-provider-observer/vb/observer.vb	Add refreshed VB observer sample (temperature reporter) with snippet markers.
docs/standard/events/snippets/shared/how-to-provider-observer/vb/data.vb	Add refreshed VB temperature data type with snippet markers.
docs/standard/events/snippets/shared/how-to-provider-observer/csharp/temperaturemonitorcs.csproj	Add new docs-local C# snippet project targeting net10.0 for the provider/observer how-tos.
docs/standard/events/snippets/shared/how-to-provider-observer/csharp/provider.cs	Add refreshed C# provider sample (temperature monitor) with snippet markers.
docs/standard/events/snippets/shared/how-to-provider-observer/csharp/program.cs	Add refreshed C# program that runs the async temperature sample.
docs/standard/events/snippets/shared/how-to-provider-observer/csharp/observer.cs	Add refreshed C# observer sample (temperature reporter) with snippet markers.
docs/standard/events/snippets/shared/how-to-provider-observer/csharp/data.cs	Add refreshed C# temperature data type with snippet markers.
docs/standard/events/snippets/observables/vb/Observables.vbproj	Add VB snippet project for the observables (baggage) sample targeting net10.0.
docs/standard/events/snippets/observables/vb/Program.vb	Add VB program entry point for the baggage sample.
docs/standard/events/snippets/observables/vb/BaggageInfo.vb	Add VB baggage info type (with equality support).
docs/standard/events/snippets/observables/vb/BaggageHandler.vb	Add VB provider implementation for baggage notifications.
docs/standard/events/snippets/observables/vb/ArrivalsMonitor.vb	Add VB observer implementation for displaying arrivals.
docs/standard/events/snippets/observables/vb/Unsubscriber.vb	Add VB unsubscriber implementation for observables sample.
docs/standard/events/snippets/observables/Unsubscriber.cs	Remove legacy shared C# unsubscriber (replaced by language-specific versions).
docs/standard/events/snippets/observables/Program.cs	Remove legacy shared C# program (replaced by language-specific versions).
docs/standard/events/snippets/observables/BaggageHandler.cs	Remove legacy shared C# baggage handler (replaced by language-specific versions).
docs/standard/events/snippets/observables/ArrivalsMonitor.cs	Remove legacy shared C# arrivals monitor (replaced by language-specific versions).
docs/standard/events/snippets/observables/csharp/Observables.csproj	Update C# observables snippet project to target net10.0.
docs/standard/events/snippets/observables/csharp/Program.cs	Add C# program entry point for the baggage sample.
docs/standard/events/snippets/observables/csharp/BaggageInfo.cs	Add C# baggage info record struct.
docs/standard/events/snippets/observables/csharp/BaggageHandler.cs	Add C# provider implementation for baggage notifications.
docs/standard/events/snippets/observables/csharp/ArrivalsMonitor.cs	Add C# observer implementation for displaying arrivals.
docs/standard/events/snippets/observables/csharp/Unsubscriber.cs	Add C# unsubscriber implementation for observables sample.
docs/standard/events/observer-design-pattern.md	Refresh article content and switch snippet references to the new docs-local snippet paths.
docs/standard/events/observer-design-pattern-best-practices.md	Refresh best practices guidance and update metadata.
docs/standard/events/how-to-implement-an-observer.md	Refresh observer how-to steps and switch to the shared docs-local snippets.
docs/standard/events/how-to-implement-a-provider.md	Refresh provider how-to steps and switch to the shared docs-local snippets.

[BillWagner]

This LGTM overall. I had a few small suggestions to consider.

[adegeo]

As discussed, SyncLock doesn't actually support the Lock type.