Refine DocumentsUI Theme to inherit Theme.DeviceDefault.DocumentsUI

Re-define theme structure to support RRO for OEM to customize
1)Allow OEM customize DocumentsTheme by RRO
2)Move night mode resource to corresponding qualifier

Test: manual to check all UI widget looks same as before
Test: atest DocumentsUITests
Change-Id: I25c7cc011d82bddb44c13234f052993d57bf221c
Fix: 118901364