[clang] [Clang] Optimize some `getBeginLoc` implementations (PR #141058)

[Aaron Ballman via cfe-commits]

AaronBallman wrote:

> https://llvm-compile-time-tracker.com/compare.php?from=f4cebe5d73c24ab53917bd58aedc9db892a164ae&to=99d11a55c0222e8ed64aa35a068a3f08673baaba&stat=instructions%3Au

There is so much green!

https://github.com/llvm/llvm-project/pull/141058