gccrs: Refactor BaseType, InferType and ErrorType impl into cc file

gccrs: Refactor BaseType, InferType and ErrorType impl into cc file

Signed-off-by: Philip Herron <herron.philip@googlemail.com>
gcc/rust/ChangeLog:

	* typecheck/rust-tyty.cc (BaseType::BaseType): refactor
	(BaseType::~BaseType): likewise
	(BaseType::get_ref): likewise
	(BaseType::set_ref): likewise
	(BaseType::get_ty_ref): likewise
	(BaseType::set_ty_ref): likewise
	(BaseType::is_equal): likewise
	(BaseType::is_unit): likewise
	(BaseType::get_kind): likewise
	(BaseType::get_combined_refs): likewise
	(BaseType::append_reference): likewise
	(BaseType::supports_substitutions): likewise
	(BaseType::has_subsititions_defined): likewise
	(BaseType::can_substitute): likewise
	(BaseType::needs_generic_substitutions): likewise
	(BaseType::contains_type_parameters): likewise
	(BaseType::get_ident): likewise
	(BaseType::get_locus): likewise
	(InferType::InferType): likewise
	(InferType::get_infer_kind): likewise
	(InferType::get_name): likewise
	(InferType::is_concrete): likewise
	(ErrorType::ErrorType): likewise
	(ErrorType::is_unit): likewise
	(ErrorType::is_concrete): likewise
	(ErrorType::get_name): likewise
	(ErrorType::monomorphized_clone): likewise
	* typecheck/rust-tyty.h (class SubstitutionArgumentMappings): likewise