Expose ChannelReader.ReadAllAsync from non-core builds as well

[stephentoub]

I'm not sure why we didn't fix this before when we shipped Microsoft.Bcl.AsyncInterfaces, but with IAsyncEnumerable available downlevel, there's no need to hide this method away; it can be in all builds. Doing so makes it easier for others to create their own channel implementations, as they don't need to multitarget in order to override everything they might want to.

I've not changed any C# code, just moved it between files.

[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, 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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I'm not sure why we didn't fix this before when we shipped Microsoft.Bcl.AsyncInterfaces, but with IAsyncEnumerable available downlevel, there's no need to hide this method away; it can be in all builds. Doing so makes it easier for others to create their own channel implementations, as they don't need to multitarget in order to override everything they might want to.

I've not changed any C# code, just moved it between files.

Author:	stephentoub
Assignees:	stephentoub
Labels:	area-System.Threading.Channels, new-api-needs-documentation
Milestone:	-

[stephentoub]

Thanks, @ViktorHofer. Fixed.