contexthub: create HubServiceInfo and associated with EndpointSession

- Create HubServiceInfo Parcelable that describes a service
- Add @Nullable argument to open session request/callback for
  HubServiceInfo
- Add HubEndpointSession.getServiceInfo -> HubServiceInfo
- Documentation adjustments

Test: build
API-Coverage-Bug: 377554469
Bug: 375487784
Flag: android.chre.flags.offload_api
Change-Id: I4b6dc1ff82fc2f3146a94080a092a30669842972