[Floss] Modify scanner callbacks

Aligning with the change in Floss daemon
(https://r.android.com/2459169), this modifies scanner callbacks:

* Wire OnAdvertisementFound to
  BluetoothLowEnergyScanSession::OnDeviceFound.
* Add plan to rename OnScanResultLost to OnAdvertisementLost for
  symmetry. Will be in future change since this needs to be coordinated
  with Floss daemon change.
* Modify OnScanResult to only update device properties and not wire it
  to OnDeviceFound.

Bug: b:269343922

Change-Id: I8253217d41f15d8d933c52d796293659992b9610
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/4295757


Reviewed-by: Katherine Lai <laikatherine@chromium.org>
Commit-Queue: Sonny Sasaka <sonnysasaka@chromium.org>
Cr-Commit-Position: refs/heads/main@{#1112862}