Trivial relocatability follow up

[cor3ntin]

• Deprecate __builtin_trivially_relocate
• Enforce that [[trivial_abi]] is applied only to relocatable types
• Add logic to static assert / overload resolution diagnostics to explain why a type is no relocatable
• Detect incorrect uses of memcpy on non-bitwise-copyable types

[llvmbot]

@llvm/issue-subscribers-clang-frontend

Author: cor3ntin (cor3ntin)

- [ ] Deprecate `__builtin_trivially_relocate` - [ ] Enforce that `[[trivial_abi]]` is applied only to relocatable types - [ ] Add logic to static assert / overload resolution diagnostics to explain _why_ a type is no relocatable

[cor3ntin]

#138835

[cor3ntin]

#141238

[cor3ntin]

The pr for memcpy warnings is #139104 , but I do plan to wait a bit before merging that