os/os2: add get_executable_path and get_executable_directory

core/sys/darwin/dyld.odin

@@ -0,0 +1,7 @@
+package darwin
+
+foreign import system "system:System.framework"
+
+foreign system {
+	_NSGetExecutablePath :: proc(buf: [^]byte, bufsize: ^u32) -> i32 ---
+}