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

[Justin Bogner via cfe-commits]

bogner 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();

I agree, but I think changes to how we check if these are implicit will have to wait for that PR and/or the PRs that actually implement implicit bindings and come along with them. In its current form, there is no `isImplicit` to check, so we're doing all that we can.

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