Un-obsolete extension ITypeSymbol APIs

[jjonescz]

Resolves #82148 per yesterday's API review decision.

[jaredpar]

Is the intent for tis to be permanent or is it being done temporarily to unblock boot strapping?

[jjonescz]

Is the intent for tis to be permanent or is it being done temporarily to unblock boot strapping?

Permanent. The potential problems with removing this later seem to outweigh the benefits. There is nothing wrong with having the APIs on ITypeSymbol, so API review decided we can just have them there permanently.

[jcouv]

LGTM Thanks (commit 1)

[jaredpar]

Is this related to #82131 where we're now marking all new APIs as experimental?

[jcouv]

Is this related to #82131 where we're now marking all new APIs as experimental?

Yes, moving forward, we're planning to have APIs related to preview features to be marked as experimental until we stamp a new language version as released. In that release, we'll consider the APIs as shipped and no longer experimental. This should avoid a customer accidentally taking a dependency on an API for a feature while still in preview.

[agocke]

Yes, moving forward, we're planning to have APIs related to preview features to be marked as experimental until we stamp a new language version as released

This will be super useful. Now we can pragma suppress during development then do a scan before we ship that we don’t have any suppressions.