Deprecating a type parameter doesn't warn when the parameter is used.

[rrousselGit]

Describe the issue

In some cases, a package may want one class to stop being used with generics.
For example, Riverpod refactored Ref<StateT> to just Ref.

This change is done with:

+@optionalTypeArgs
class Ref<
+  @deprecated
  T> {}

The problem is, existing references to the type parameter does not cause a warning.

To Reproduce

@optionalTypeArgs
class Ref<@deprecated  T> {}

Ref<int>? value; 

Expected behavior

This should warn on <int> that the type parameter is deprecated

[bwilkerson]

That seems reasonable, at least for the case where all of the type parameters are deprecated.

If some are deprecated and others are not then I don't think it helps to produce the warning because it isn't actionable.