gccrs: Insert imports in all namespaces they were resolved in

gccrs: Insert imports in all namespaces they were resolved in

gcc/rust/ChangeLog:

	* resolve/rust-early-name-resolver-2.0.cc (Early::resolve_simple_import):
	Insert import in all namespaces where they were resolved.
	(Early::resolve_rebind_import): Likewise.
	* resolve/rust-early-name-resolver-2.0.h: Improve APIs, make them
	accept multiple resolutions.
	* resolve/rust-finalize-imports-2.0.cc: Handle multiple resolutions.
	* resolve/rust-name-resolution-context.h (resolve_path): Remove function.