[clang] [analyzer][Z3][NFCI] Simplify getExpr* functions by taking a RetTy reference (PR #180801)

[Ella Ma via cfe-commits]

https://github.com/Snape3058 approved this pull request.

LGTM, thank you for the fix.
I run the test cases locally on my machine, and all pass.

But while running the test cases, I found another problem with the execution of test cases that requires z3. I will pose another issue and pr later.

https://github.com/llvm/llvm-project/pull/180801