Restore a (tweaked) version of the DND slice

DndModeSliceBuilder is a fork of ZenModeSliceBuilder, with a more appropriate name, and the following changes:
* Uses ZenModesBackend in order to toggle DND exclusively without affecting other modes
* Listens to a (new) broadcast because INTERRUPTION_FILTER_CHANGED doesn't mesh well with the previous item
* Intent redirects to the mode page for DND (instead of the old DND page)
* Some other code renamed to match, except for "public API" like the URI

Bug: 406238205
Flag: android.app.modes_ui_dnd_slice
Test: atest DndModeSliceBuilderTest + manual
Change-Id: I6d813e229846fe63092a8b63ec394f2d854bc672