Add overlayable.xml to define customization scope

1) Define overlayable scope in DocumentsUI
2) Define android:targetName="DocumentsUIThemeOverlay" for overlay package
3) Fix Drawer selector visual issue

Change-Id: Ided1e26b5a732a327107f3d597ed7e5e96e86d5f
Fix: 127615752
Fix: 128502868
Test: atest DocumentsUIGoogleTests
9 files changed