Create framework for initial content pane focus

Per new UX guidance, the content pane should get the initial rotary
focus for most settings journeys, with the exception being launching
the settings homepage (either from the launcher or from quick
settings). This behavior can be customized per activity by overriding
the relevant method.

Bug: 191185344
Test: manual, atest CarSettingsUnitTests
Change-Id: I3dfc557801f1affb24332210b7f12656f26fe038
5 files changed