[clang] [CIR][ABI] Add restrict, nonnull, and ReturnsNonNull attributes (PR #188281)

[via cfe-commits]

adams381 wrote:

Addressed all feedback in the latest push:

- Moved ReturnsNonNullAttr to constructFunctionReturnAttributes, added NullPointerIsValid guard
- Skipped restrict→noalias for builtins (printf was getting noalias from its restrict param, OGCG doesn't)
- Tightened OGCG checks on operator new calls in new-delete.cpp

https://github.com/llvm/llvm-project/pull/188281