Roslyn: Permit a trailing comma inside a switch expression

[gafter]

Per LDM 2019-01-09 we have accepted the proposal in https://github.com/dotnet/csharplang/issues/2098 to allow a trailing comma inside a switch expression
``` c#
_ = e switch
{
1 => 2,
3 => 4, // comma now allowed here
}

Similarly, we have accepted a proposal to allow a trailing comma inside a property subpattern.
``` c#
_ = e is T
    {
        X: 2,
        Y: 3, // comma now allowed here
    };

This needs to be implemented.

[CyrusNajmabadi]

Thanks!

[alrz]

what about property patterns?

[gafter]

https://en.wikipedia.org/wiki/Whataboutism ;)

[gafter]

@alrz Yes, inside property patterns too (approved yesterday).

[CyrusNajmabadi]

Awesome!