contexthub: add new getHubs hidden API for V4

- Add hidden API ContextHubManager.getHubs() -> HubInfo
- HubInfo is a union type for VendorHubInfo (newly introduced) and
  ContextHubInfo
- Create HubInfoRegistry for tracking hub and endpoint info

Refactor
- Renamed getHubs to getContextHubs for some internal methods

Sample dumpsys for HubInfo: https://paste.googleplex.com/4989897428697088?raw

Test: manual
Bug: 375487784
Flag: android.chre.flags.offload_api
Change-Id: I841ff14b5378fc1d4df3a0c6b0e6fc082a189059