Razor source generator incrementality goes wrong on downgrades

[SteveSandersonMS]

This is to track fixing the issue identified at dotnet/sdk#15756 (review)

The most likely case where this affects someone is when downgrading to an older dependency, but would also affect them when upgrading to one that's already cached locally.

[ghost]

I couldn't figure out the best area label to add to this issue. If you have write-permissions please help me learn by adding exactly one area label.

[pranavkm]

This should be a good way to track that the specific issue gets fixed. Also we're continuing to use the AspNetCore repo to track SDK issues, so moved this over.

[ghost]

Thanks for contacting us.
We're moving this issue to the Next sprint planning milestone for future evaluation / consideration. We will evaluate the request when we are planning the work for the next milestone. To learn more about what to expect next and how this issue will be handled you can read more about our triage process here.

[captainsafia]

Closing this in favor of #30234.

We're moving to an in-memory cache model which will remove this particular codepath. Instead, we'll be determining whether or not to cache-bust based on a unique identifier associated with each metadata reference.