[clang] [Clang][Sema][NFCI] Simplify `resolveAllocationOverload()` (PR #203824)

[Igor Kudrin via cfe-commits]

igorkudrin wrote:

> I would _really_ like to get rid of the operations over stack allocated AST nodes.

This deserves its own atomic patch, separate from other changes, no?

https://github.com/llvm/llvm-project/pull/203824