[llvm] [X86][GlobalISel] Reorganize shift scalar tests (NFC) (PR #68232)

[Evgenii Kudriashov via llvm-commits]

e-kud wrote:

Basically, moved `llvm/test/CodeGen/X86/fast-isel-shift.ll` to `llvm/test/CodeGen/X86/isel-shift.ll` with checking all three selectors and removed duplicates from `llvm/test/CodeGen/X86/GlobalISel`.

https://github.com/llvm/llvm-project/pull/68232