[ClangImporter] Look through bounds attributes for template matching

[hnrklssn]

When instantiating templated functions with pointers to the templated type, the ClangImporter does not strip type sugar. This strips type sugar for bounds attributes, to make sure that they import the same regardless of whether they are parsed or not.

rdar://151041990

[hnrklssn]

@swift-ci please smoke test

[hnrklssn]

These functions all contain this type of pattern:

if (isa<clang::PointerType>(paramTy) &&
             isa<clang::TemplateTypeParmType>(paramTy->getPointeeType())) {

My hunch is that they actually ought to use something like this (or equivalent with getAsAdjusted):

if (paramTy->getAs<clang::PointerType>() &&
             paramTy->getAs<clang::PointerType>()->getPointeeType()->getAs<clang::TemplateTypeParmType>() {

But I don't want to introduce unnecessary risk this late in the release cycle, so I elected to only strip the type sugar we know we need to strip, in case it affects other things. Especially since it seems like this template logic is all a bit of a hack anyways that eventually needs to be replaced; e.g. this doesn't seem to get imported:

template <class T>
void foo(T **p);

CC @egorzhdan in case you have more context