[Blazor] Flow the WebAssembly options from Server to client through SSR marker

[maraf]

We won't be able to use HTTP headers after migration of boot config to ES module. The PR moves EnvironmentName, DOTNET_MODIFIABLE_ASSEMBLIES and __ASPNETCORE_BROWSER_TOOLS environment variables from custom HTTP headers on boot config request to SSR marker produced during server rendering.

It doesn't affect standalone mode as there is no server to write these values to.

The prerendered comment looks like

<!--Blazor-WebAssembly:{"environmentName":"Development", "environmentVariables":{"DOTNET_MODIFIABLE_ASSEMBLIES": "true","__ASPNETCORE_BROWSER_TOOLS":"true}}-->

Contributes to #59456

PR Overview

This PR changes the mechanism for transmitting WebAssembly runtime settings by shifting from custom HTTP headers to embedding the settings within an SSR marker. Key changes include:

• Introducing a new WebAssemblySettingsEmitter that captures environment variables on the server.
• Modifying both server-side and JavaScript boot and discovery routines to process and propagate these settings via SSR markers.
• Removing legacy conventions for WebAssembly HTTP response header management.

Reviewed Changes

File	Description
src/Components/Endpoints/src/DependencyInjection/WebAssemblySettingsEmitter.cs	New emitter implementation to capture and expose WebAssembly environment settings.
src/Components/Endpoints/src/Rendering/EndpointHtmlRenderer.Streaming.cs	Embeds the settings JSON into the SSR marker during rendering.
src/Components/Web.JS/src/Services/ComponentDescriptorDiscovery.ts	Adds regex and discovery function for extracting WebAssembly options from SSR markers.
src/Components/Endpoints/src/DependencyInjection/RazorComponentsServiceCollectionExtensions.cs	Registers the new WebAssemblySettingsEmitter in DI.
src/Components/Web.JS/src/Boot.WebAssembly.Common.ts	Updates methods to accept and propagate WebAssembly options to the runtime.
src/Components/Web.JS/src/Boot.WebAssembly.ts	Extracts and passes WebAssembly options to the startup routine.
src/Components/Web.JS/src/Services/WebRootComponentManager.ts	Captures discovered WebAssembly options and passes them along during component registration.
src/Components/Web.JS/src/Rendering/DomMerging/DomSync.ts	Updates the descriptor handler interface to include the WebAssembly options.
src/Components/WebAssembly/Server/src/Builder/WebAssemblyRazorComponentsEndpointConventionBuilderExtensions.cs	Removes the legacy call to add Blazor WebAssembly conventions.
src/Components/WebAssembly/Server/src/ComponentWebAssemblyConventions.cs	Legacy file removed as the functionality is now handled by the SSR marker.

Copilot reviewed 10 out of 10 changed files in this pull request and generated no comments.

Comments suppressed due to low confidence (1)

src/Components/Web.JS/src/Services/ComponentDescriptorDiscovery.ts:18

• The regex for extracting WebAssembly options may be too permissive if the SSR marker comment format changes. Consider tightening the pattern (for example, by explicitly matching the opening '{') to ensure the 'options' group reliably captures a valid JSON object.

const blazorWebAssemblyOptionsCommentRegularExpression = /^\s*Blazor-WebAssembly:[^{]*(?<options>.*)$/;

[javiercn]

Looks great!

[pavelsavara]

Could you please add example of generated HTML to the description, thanks!