Overhaul the message senders screen

* Fix combinations of messages=all with other conversation values.
* Correctly display policies with CONVERSATION_SENDERS_ANYONE. An additional checkbox is included, but _only_ if the policy has CONVERSATION_SENDERS_ANYONE when shown.
* Changed updateState() to consider the possible cases one by one. Because multiple policies are mapped to the same checkbox states, the strategy of "checking whether the state matches what the checkbox wants to set" doesn't really work.
* Fix messages summary and circles to support CONVERSATION_SENDERS_ANYONE.
* Added a lot of tests (actually, hopefully ALL OF THEM) covering the user-visible behavior. :)

Fixes: 354658240
Test: atest ZenModesSummaryHelperTest ZenModePrioritySendersPreferenceControllerTest
Flag: android.app.modes_ui
Change-Id: I727496ca3eb820e4baaab942b61d2e57cdb491fc