DocsUI M3: Move menu folder for flag material3 disabled

This is a preparation to customize the app bar for Material3, because
menus are used in the app bar.

Test: Manual build, deploy apk and start it on DUT with flag off
Flag: com.android.documentsui.flags.use_material3
Bug: 377771271, 377771946
Change-Id: Ia1882f4e5fce7d2b803b456e4fe72552a75eb211