[clang] [CIR] Upstream RTTI Builder & RTTI for VTable Definitions (PR #160002)

[Amr Hesham via cfe-commits]

AmrDeveloper wrote:

Notes:

- Anything inside the anonymous namespace will be removed after https://github.com/llvm/llvm-project/pull/157936 lands, and import the same code either from the new shared component or the AST/basics lib

https://github.com/llvm/llvm-project/pull/160002