[clang] [clang] Add value_type attr, use it to add noalias when pass-by-value. (PR #95004)

[Nikolas Klauser via cfe-commits]

philnik777 wrote:

This is really sweet. However, I feel like this is a property that needs to propagate through types. We can't guarantee that a `std::vector<int, my_nasty_allocator<int>>` doesn't escape the pointer. Similarly, I think we'd like
```c++
struct my_pair {
  int i;
  std::string str;
};
```
to have this property.

https://github.com/llvm/llvm-project/pull/95004