[clang] [clang][Analysis] Add argument accessors to clang::AnyCall (PR #212934)

[Gábor Horváth via cfe-commits]

https://github.com/Xazax-hun commented:

I think this looks solid, thanks!

If it is not too much work to add a test it would be great! Otherwise, if it starts to get out of hand, I think it might be fine to say that this will be used and tested indirectly in a follow-up PR. 

https://github.com/llvm/llvm-project/pull/212934