SecurityManager: Classic Pairing Handler

- Plumbing for driving pairing handler and foundation for Classic Pairing Logic
- Implement JustWorks Association models and unit tests

Bug: 144374435 144376172
Test: atest --host -t bluetooth_test_gd:ClassicPairingHandlerTest
Change-Id: Ie88956602e14567f32eaa0f6ca397521d398e1ab