Make sure that the usage of `cppType` and `cppClassName` of type and
attribute definitions/constraints is consistent in TableGen.
- `cppClassName`: The C++ class name of the type or attribute.
- `cppType`: The fully qualified C++ class name: C++ namespace and C++
class name.
Basically, we should always use the fully qualified C++ class name for
parameter types, return types or template arguments.
Also some minor cleanups.
Fixes#57279.
35f55f53df