gccrs: Add missing hir lowering to function type-path segments

gccrs: Add missing hir lowering to function type-path segments

gcc/rust/ChangeLog:

	* Make-lang.in: Compile rust-ast-lower-type.cc.
	* ast/rust-path.h: Add `get_locus` method to `TypePathFunction`.
	* hir/rust-ast-lower-base.cc (ASTLowerTypePath::visit): Move implementation to
	rust-ast-lower-type.cc.
	(ASTLowerQualifiedPathInType::visit): Likewise.
	(ASTLoweringType::visit): Likewise.
	* hir/rust-ast-lower-type.h: Move implementations to source file.
	* hir/tree/rust-hir-path.h: Likewise.
	* hir/rust-ast-lower-type.cc: New file.