Tablegen would generate code to access TargetResourceIndices with
processor ID.
The TargetProcResourceIndexStart[] array is generated for each processor
which has itineraries. The processor which doesn't has itineraries is excluded
from the array. When a target has mixed processors, the processor ID may
exceed the array size and cause the error.
This patch is to generate a table mapping processor with itineraries to
resource index, so that scheduler can get the correct resource index with
processor ID.

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

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

---------

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

Change `getValueAsListOfDefs` to return a vector of const Record
pointer, and remove `getValueAsListOfConstDefs` that was added as a
transition aid.

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 DFAPacketizerEmitter 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 CodeGenSchedule to use const Record 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

Change CodeGenSchedule 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

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