[clang] [HLSL] Add a warning for implicit bindings (PR #135909)

[Joshua Batista via cfe-commits]

bob80905 wrote:

As a general comment, your approach of just checking for the existence of the binding attribute may not in itself be sufficient.
Consider this PR:
https://github.com/llvm/llvm-project/pull/135287/files
There is a potential case where the binding attribute has a slot = -1, signifying that it is implicit.
This PR may need to account for Helena's, because if a binding attribute can exist and also signify implicitness, the proper condition to check for explicitness assuming attribute existence is probably:
Attr->isImplicit();

https://github.com/llvm/llvm-project/pull/135909