[DocsUI M3] Fix the focus issue inside drawer layout

Disable the focusability of the main container (e.g. app bar and file
list) when the drawer is open, so the focus will be locked inside the
drawer, restore it when the drawer is closed.

Check the attached bug for demo.

Bug: 370628223, 423152273
Test: atest DocumentsUIGoogleTests:com.android.documentsui.KeyboardNavigationUiTest#testKeyboard_arrowsRootsList
Test: atest DocumentsUIGoogleTests:com.android.documentsui.KeyboardNavigationUiTest#testKeyboard_tabCycleInRootsList
Flag: com.android.documentsui.flags.use_material3
Change-Id: I05bbeca37c6327104f7dffbfe4cc653c9856f945