[clang-tools-extra] [analyzer] Split alpha core Identical Expression tests (PR #119543)

[Julian Schmidt via cfe-commits]

5chmidti wrote:

The file-names should follow the naming convention of the other tests: `checkers/misc/redundant-expression.cpp` (applies to both). 

@HerrCai0907  @PiotrZSL IMO merging these tests with the existing ones would result in too-large files, so the files would probably be named something like `redundant-expression-2.cpp`. WDYT?

https://github.com/llvm/llvm-project/pull/119543