Adding Microsoft.Bcl.AsyncInterfaces for .NET Standard 2.0

[joperezr]

cc: @stephentoub @ericstj @Petermarcu @maririos @terrajobst

This is adding the package which contains all of the Async interfaces OOB implementation as well as the netcoreapp3.0, uapvnext and netstandard2.1 facades.

[stephentoub]

Microsoft.Compatibility.AsyncInterfaces

Is this a place-holder name, or is this what @terrajobst has decided on?

[joperezr]

Is this a place-holder name, or is this what @terrajobst has decided on?

@terrajobst hasn't yet approved this name, this is just what made more sense for now, but I'm happy to change it in the PR if Immo wants to change it.

[joperezr]

Just as FYI @terrajobst other one that was considered was Microsoft.Compatibility.AsyncEnumerables

[Petermarcu]

/cc @KrzysztofCwalina @pakrym as FYI

[stephentoub]

Thanks, @joperezr!

[terrajobst]

This looks great, thanks @joperezr. I've only marked this as request changes so we don't merge yet. I've set up a meeting to discuss a few architectural items which we need to get clarity on before picking a name here (you're on the invitee list @joperezr).

Basically, we need to differentiate things like immutable which can be evolved (because they can replace the in-box module wholesale) from things like IAE which can't be evolved (becaue they type forward to modules we can't replace).

[KrzysztofCwalina]

Could we name it somehow that would not scare people? IMO, the ideal name would be System.Extensions.Async (or something like that). Microsoft.Extensions.Async would be acceptable.

[terrajobst]

Could we name it somehow that would not scare people?

We need to convey that new code doesn’t need these packages ever. They should use the inbox version. The ‘System’ name doesn’t convey this.

[joperezr]

This is now ready to go

[terrajobst]

One minor edit, otherwise LGTM.

[stephentoub]

Thanks!