Runtime: Add .NET 4.6.1 target to AsyncInterfaces

[clairernovotny]

The AsyncInterfaces package currently targets .NET Standard 2.0 and .NET Standard 2.1. This means that a .NET Framework 4.6.1 project may pull in a lot of other packages by referencing this one.

Please add a .NET 4.6.1 target (with the same items as in the .NET Standard 2.0 one) to minimize package dependency issues.

[karelz]

@joperezr @stephentoub any thoughts?

[stephentoub]

any thoughts?

What's the downside of adding a 4.6.1 target? "Just" increased size of the NuGet package?

@terrajobst, any strong reason not to do this? Presumably if we did, we'd do it for all of the recently added packages?

[joperezr]

AFAIK there are no other concerns apart from nuget package size and to actually make the source compile against netfx.

[joperezr]

I'll take care of this.

[tarekgh]

@joperezr would you do that for all recently added packages?

[joperezr]

would you do that for all recently added packages?

Nope, the plan is to do it for the 3 bridge packages, which are all includded in my PR dotnet/corefx#38104. Is there a specific package you want to have a net461 target?