DocsUI M3: Move flag disabled resources to res root

This allows both themes Material3 and pre-material3 to co-exist in the
APK.

The resources for Material3 have gotten the `m3` suffix added and
references to them have been updated to use the suffix or switch to M3
version using `ThemeUtils.getRes()` in Java/Kotlin code.

Bug: 403375773
Test: m DocumentsUIGoogle && manual inspection
Flag: com.android.documentsui.flags.use_material3
BYPASS_LARGE_CHANGE_WARNING: Mostly moving code around

Change-Id: I9128fe7675737695ff216771e630c62bf9e407ec