os/os2: recursive directory walker, expose errors in read_directory, file clone

Adds a directory walker, a method of exposing and retrieving errors from
the existing read directory iterator, allows reusing of the existing
read directory iterator, and adds a file clone procedure

core/os/os2/file.odin

@@ -122,6 +122,11 @@ new_file :: proc(handle: uintptr, name: string) -> ^File {
 	return file
 }
 
+@(require_results)
+clone :: proc(f: ^File) -> (^File, Error) {
+	return _clone(f)
+}
+
 @(require_results)
 fd :: proc(f: ^File) -> uintptr {
 	return _fd(f)