[clang] [SSAF] Extract the virtual method override relation per TU (PR #213316)

[Balázs Benics via cfe-commits]

steakhal wrote:

> I'd like to see a test where class A inherits class B and B inherits class C. The base class C has a virtual function `f` being overridden by both A and B. Is `C::f` in `A::f`'s overridden methods?

Added in https://github.com/llvm/llvm-project/pull/213316/commits/5e98d1a82e052ea50f1736984fdbbe161712d6d4.

> On a separate note: each of our SSAF unit test files has its own ad-hoc utility functions for conveniently getting an entityId or an AST node from a readable name. At some point, we may want to have a good general solution for this. Maybe all of them should use ParsedAST.h.

100% agree. It was a major source of friction for me as well. We could discuss this later and refactor all tests.

https://github.com/llvm/llvm-project/pull/213316