Detect misuse of [[clang::noescape]] annotation

[usx95]

std::string_view foo(const std::string& in [[clang::noescape]]) {
  return in;
}

e.g.: in escapes through return but is marked noescape.

After #169767, the placeholder loans can help detect when parameters escape. Currently we suggest to add lifetimebound to such params. But when the param is annotated with clang::noescape, we should diagnose a misuse.

[llvmbot]

@llvm/issue-subscribers-clang-temporal-safety

Author: Utkarsh Saxena (usx95)

``` std::string_view foo(const std::string& in [[clang::noescape]]) { return in; } ``` e.g.: `in` escapes through `return` but is marked `noescape`.

After #169767, the placeholder loans can help detect when parameters escape. Currently we suggest to add lifetimebound to such params. But when the param is annotated with clang::noescape, we should diagnose a misuse.