[Alignment][NFC] Add DebugStr and operator*

Summary:
This is a roll forward of D77394 minus AlignmentFromAssumptions (which needs to be addressed separately)
Differences from D77394:
 - DebugStr() now prints the alignment value or `None` and no more `Align(x)` or `MaybeAlign(x)`
   - This is to keep Warning message consistent (CodeGen/SystemZ/alloca-04.ll)
 - Removed a few unneeded headers from Alignment (since it's included everywhere it's better to keep the dependencies to a minimum)

Reviewers: courbet

Subscribers: sdardis, hiraditya, jrtc27, atanasyan, llvm-commits

Tags: #llvm

Differential Revision: https://reviews.llvm.org/D77537