* Fix warnings for DAM.All

Fixes #2159

* Add tests

* PR feedback

- Remove unnecessary helper

* Avoid redundant DAM warnings for base members

* PR feedback

- Resolve -> TryResolve
- Avoid nested yield returns
- Testcases with base instantiated over self for generic parameter with
  requirements

* Fix suppression check with assembly suppressions

The change in #2171 was incorrect
because it didn't account for the possibility that the suppressions
cache already contains assembly or module suppressions for the provider.

This fixes the check by re-using the cache to also track whether we have
scanned for suppression attributes on the provider. This caching is
necessary since we warn about duplicate suppressions.

Providers without any suppressions may still be scanned multiple times
since we don't cache the negative result.

* Populate cache eagerly to avoid extra state

Now whenever we add a record to the cache, we ensure that all of the
suppressions that might apply to the member have been discovered.
This way we don't need to track whether we have scanned the suppressed
member, but have to do a bit more work up-front.

* Use private accessibility

For methods only used in
UnconditionalSuppressMessageAttributeState