Rename `ListInit::getValues()` to `getElements()` to better match with
other `ListInit` members like `getElement`. Keep `getValues()` for
existing downstream code but mark it deprecated.

- Also eliminate unneeded std::string() around some literal strings.

- Emit C++17 nested namespaces.
- Shorten the binary search table name to just `Table` since its
declared in the scope of each search function.
- Use `using namespace XXX` in the search function to avoid emitting the
Target Inst Namespace prefix in the table entries.
- Add short-cut handling of `TableSize` == 0 case (verified in Hexagon
target).
- Use `SetVector` in `ColFieldValueMap` to get automatic deduplication
and eliminate manual deduplication code.
- Use range for loops.

Code cleanups for TableGen files, changes includes function names,
variable names and unused imports.

---------

Co-authored-by: Matt Arsenault <Matthew.Arsenault@amd.com>

This is a part of effort to have better const correctness in TableGen
backends:


https://discourse.llvm.org/t/psa-planned-changes-to-tablegen-getallderiveddefinitions-api-potential-downstream-breakages/81089

Change CodeGenMapTable to use const RecordKeeper.

This is a part of effort to have better const correctness in TableGen
backends:


https://discourse.llvm.org/t/psa-planned-changes-to-tablegen-getallderiveddefinitions-api-potential-downstream-breakages/81089

Change CodeGenInstruction::{TheDef, InfereredFrom} to const pointers.

This is a part of effort to have better const correctness in TableGen
backends:


https://discourse.llvm.org/t/psa-planned-changes-to-tablegen-getallderiveddefinitions-api-potential-downstream-breakages/81089

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

```
find llvm/utils/TableGen -iname "*.h" -o -iname "*.cpp" | xargs clang-format-16 -i
```

Split from #80847