Fix checking for type parameter visibility when merged with a parameter

[weswigham]

Fixes #25672

A type parameter merged with a parameter has both type and value meanings, and both the Type and the Value masks contain some of the same meanings (Class, Enum, EnumMember and Assignment), so comparing a target meaning (and not a flags member) against just one of them almost always yields true. We really only want to limit the scope of the parameter meanings of the symbol to the function body, so we need to ensure that the meaning we're looking for is really just the value meanings we actually care about (in this case, FunctionScopedVariable).