Adds extension method to create service scope that implements IAsyncDisposable.

[bjorkstromm]

• Introduces a new type AsyncServiceScope that implements IServiceScope and IAsyncDisposable. The type just wraps an existing IServiceScope instance, which it tries to cast it to an IAsyncDisposable when DisposeAsync is called.
• Adds netstandard2.1 target to avoid bringing in System.Threading.Tasks.Extensions and Microsoft.Bcl.AsyncInterfaces if not needed.
• Fixes Make CreateScope return ServiceScope that also implements IAsyncDisposable #43970

Can't remember (nor find info) whether we agreed on putting this in Microsoft.Extensions.DependencyInjection or Microsoft.Extensions.DependencyInjection.Abstractions. I added it to Microsoft.Extensions.DependencyInjection.Abstractions, which however only targeted net461 and netstandard2.0. This means that we have to pull in System.Threading.Tasks.Extensions (for ValueTask) and Microsoft.Bcl.AsyncInterfaces (for IAsyncDisposable). Because of this, I think it would be wise to add a netstandard2.1 target so that these dependencies can be ignored on net5 and newer,

// cc @davidfowl

[ghost]

Note regarding the new-api-needs-documentation label:

This serves as a reminder for when your PR is modifying a ref *.cs file and adding/modifying public APIs, to please make sure the API implementation in the src *.cs file is documented with triple slash comments, so the PR reviewers can sign off that change.

[ghost]

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Issue Details

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• Introduces a new type AsyncServiceScope that implements IServiceScope and IAsyncDisposable. The type just wraps an existing IServiceScope instance, which it tries to cast it to an IAsyncDisposable when DisposeAsync is called.
• Adds netstandard2.1 target to avoid bringing in System.Threading.Tasks.Extensions and Microsoft.Bcl.AsyncInterfaces if not needed.
• Fixes Make CreateScope return ServiceScope that also implements IAsyncDisposable #43970

Can't remember (nor find info) whether we agreed on putting this in Microsoft.Extensions.DependencyInjection or Microsoft.Extensions.DependencyInjection.Abstractions. I added it to Microsoft.Extensions.DependencyInjection.Abstractions, which however only targeted net461 and netstandard2.0. This means that we have to pull in System.Threading.Tasks.Extensions (for ValueTask) and Microsoft.Bcl.AsyncInterfaces (for IAsyncDisposable). Because of this, I think it would be wise to add a netstandard2.1 target so that these dependencies can be ignored on net5 and newer,

// cc @davidfowl

Author:	bjorkstromm
Assignees:	-
Labels:	area-Extensions-DependencyInjection, new-api-needs-documentation
Milestone:	-

[davidfowl]

This looks good but needs tests

[bjorkstromm]

This looks good but needs tests

This looks good but needs tests

Tests added to Microsoft.Extensions.DependencyInjection.Tests

[davidfowl]

LGTM

[eerhardt]

Looks good. Thanks for the contribution!

[davidfowl]

Excellent work @bjorkstromm Im looking forward to more changes like this