settings(uwb): Refactor UwbPreferenceController

1. Use handler executor to directly handle state changed callbacks in
the same thread as APM handling.
2. Use the same flow to fetch the initial APM mode & UWB state from
onStart()
3. Store the state and reason code (to be used for showing regulatory
message in follow up CL).
4. Refactor the class for better unit testing (use mocks, avoid reaching
into class members being tested by using argument captor).

Bug: 270515435
Test: Manual tests
Test: atest UwbPreferenceControllerTest
Change-Id: I1b8c06a05691d9512de65ca2d61f3963dab230ab