[clang] [clang][Sema] Track trivial-relocatability as a type trait (PR #84621)

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isidorostsa wrote:

Currently, [HPX](https://github.com/STEllAR-GROUP/hpx) implements the P1144 interface. We have our own implementation of the is_trivially_relocatable trait, but it cannot recursively figure out if a type is relocatable based on its components. It would be great for us to let the compiler handle that, as it would lead to optimizations for many more types.

https://github.com/llvm/llvm-project/pull/84621