Reland (again) D80966 [codeview] Put !heapallocsite on calls to operator new

Check that getDebugInfo() is not null, as in the first revision, before
calling getDebugInfo()->addHeapAllocSiteMetadata().
Else would cause a crash with a new expression in a default arg.

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Clang marks calls to operator new as heap allocation sites, but the
operator declared at global scope returns a void pointer. There is no
explicit cast in the code, so the compiler has to write down the
allocated type itself.

Also generalize a cast to use CallBase, so that we mark heap alloc sites
when exceptions are enabled.

Differential Revision: https://reviews.llvm.org/D80966