[llvm] LowerTypeTests: Fix quadratic complexity (try 2). (PR #136053)

[Florian Mayer via llvm-commits]

https://github.com/fmayer approved this pull request.

please confirm the `ScopedSaveAliaseesAndUsed` use on line 2063 (of RHS, 2050 of LHS) is OK with the semantics change

https://github.com/llvm/llvm-project/pull/136053