DocumentsUI: Move the styles, layout and theme for flag M3 disabled

This is a preparation to allow customizing the Material3 behind a flag
without changing the current layout and styles.

Test: Manual build, deploy apk and start it on DUT with flag on/off
Flag: com.android.documentsui.flags.use_material3
Bug: 377771271
Change-Id: Ifdea578323a613456ffcc2e146adaf6892d91ff2