[Clang] Fix concept paramater mapping and caching (#161994)
This expression is not handled by default in RAV, so our parameter
mapping and cache mechanism don't work when it appears in a template
argument list.
There are a few other expressions, such as PackIndexingExpr and
FunctionParmPackExpr, which are also no-ops by default. I don't have a
test case for them now, so let's leave those until users complain :/
There was also a bug in updating the parameter mapping, where the
AssociatedDecl was not updated accordingly.
Also also, this fixes another regression reported in
https://github.com/llvm/llvm-project/pull/161671#issuecomment-3367225480,
where we failed to account for the variable initializer in cache
profiling.
Relies on #161671
Fixes https://github.com/llvm/llvm-project/issues/161983
Fixes https://github.com/llvm/llvm-project/issues/161987