Adopt scaled indent in PredicateExpander.
Added pre/post inc/dec operators to `indent` and related unit tests.
Verified by comparing *.inc files generated by LLVM build with/without
the change.
Refactor of the llvm-tblgen source into:
- a "Basic" library, which contains the bare minimum utilities to build
`llvm-min-tablegen`
- a "Common" library which contains all of the helpers for TableGen
backends. Such helpers can be shared by more than one backend, and even
unit tested (e.g. CodeExpander is, maybe we can add more over time)
Fixes#80647
