Add VirtualStaticsInInterfaces flag to RuntimeFeature

[davidwrighton]

Based on approved api in #49905. This won't be merged until at least the coreclr runtime is capable.

[dotnet-issue-labeler]

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.

[davidwrighton]

@lambdageek Are you ok with merging this change before enabling the feature in mono? I'd prefer to get this in (and the initial coreclr implementation) before the deadline for Preview5, but if you'd prefer to hold off, that can probably also work.
@trylek fyi, when we merge the implementation of the interface static methods, this is the next thing, then crossgen2 and deciding if the feature should have default interface method support in the V1 release.

[lambdageek]

@davidwrighton yep, no need to wait for mono.

[trylek]

LGTM, thank you!