floss: Decouple set connect/discoverable functions and revise the suspend/resume code

The current code has some issues:
- On resume we only restore the previous connectable mode, but the peer
  status may have changed so trigger_update_connectable_mode would be
  preferred.
- If device was discoverable before suspend, it would be restored
  without a timeout after resume. Which means the device would be
  discoverable forever.
- Set connectable mode to false would always reset discoverable mode.
  This becomes an issue because we now adjust the connectable mode often
  and it also makes it hard to resolve the previous issues.

This patch does:
- Decouple the set connect/discoverable functions. Set connectable would
  be no-op if the device is discoverable. On discoverable timeout, the
  connectable mode would be restored.
- Implement enter/exit suspend function for scan mode. Properly handle
  the set connect/discoverable functions when device is suspending.
- Since the set connect/discoverable functions are decoupled, we could
  also prevent sending the redundant connectable mode to LibBluetooth.

Bug: 336881286
Tag: #floss
Test: mmm packages/modules/Bluetooth
Test: Tauto: SAHealth, CLHealth, SRHealth on Nipperkin upstream Floss
Test: Tauto: SAHealth, CLHealth, SRHealth on Nipperkin local Floss
Test: manual PhoneHub / SmartLock / NearbyShare HighVis / Fast Pair
Test: manual Classic peer + suspend resume
Test: manual verified a short discoverable timeout correctly reset the
      scan mode after suspend/resume
Flag: EXEMPT, Floss-only changes
Change-Id: I588b70dc6d9816cd211f9cab16ddff6f3c9ee302