Expose mlir::parseType to bindings

Python bindings currently currently provide a makeScalarType function that
constructs one of the predefined types. It was implemented in the bindings
directly to circumvent the absence of standalone type parsing function. Now
that mlir::parseType has been made available, rely on the core parsing
procedure to construct types from strings in the bindings.

This changes includes a library reshuffling that splits out "CoreAPIs"
implementing the binding helper APIs into a separate library and makes that
dependent on the Parser library.

PiperOrigin-RevId: 274794516