[clang] [Clang][Sema] Use the correct lookup context when building overloaded 'operator->' in the current instantiation (PR #104458)

[Krystian Stasiowski via cfe-commits]

sdkrystian wrote:

@cor3ntin After giving it another look, I think the existing tests are sufficient (the tests updated by this PR were written by me to test this exact scenario). WDYT?

https://github.com/llvm/llvm-project/pull/104458