[InstCombine] fix tests for adjusted min/max

1. Delete identical tests
2. Rename tests to reflect actual functionality
3. Add comments
4. Add unsigned variants
5. Add vector variants with FIXME comments
6. Rename test file


git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@285699 91177308-0d34-0410-b5e6-96231b3b80d8
2 files changed