gccrs: Refactor PathProbeType code into CC file

gccrs: Refactor PathProbeType code into CC file

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

	* typecheck/rust-hir-path-probe.cc (PathProbeCandidate::Candidate::Candidate): refactor
	(PathProbeCandidate::PathProbeCandidate): likewise
	(PathProbeCandidate::as_string): likewise
	(PathProbeCandidate::is_enum_candidate): likewise
	(PathProbeCandidate::is_impl_candidate): likewise
	(PathProbeCandidate::is_trait_candidate): likewise
	(PathProbeCandidate::is_full_trait_item_candidate): likewise
	(PathProbeCandidate::get_error): likewise
	(PathProbeCandidate::is_error): likewise
	(PathProbeCandidate::get_defid): likewise
	(PathProbeCandidate::operator<): likewise
	* typecheck/rust-hir-path-probe.h (struct PathProbeCandidate): likewise