Add buttons for new settings design

This adds a new class called PrimaryProviderPreference
which is responsible for laying out the old cog view if
the feature is disabled and the new button view if it
is enabled.

Screenshots:
https://hsv.googleplex.com/5109836204212224
https://hsv.googleplex.com/5574754636398592
https://hsv.googleplex.com/6737135727017984

Change-Id: I1ad0c59a4afc5be3694b499f66bbd7306dfbee69
Test: Manual test with flag on + off & unit tests
Bug: 300979487