PDL: Define MSFT packets in PDL

* Add MSFT packet definitions that are required for LE Scanning hardware
  offload (Advertisement Monitor).
* Add gn build definition for HCI-related unit tests.

Bug: 217274009
Tag: #floss
Test: bluetooth_test_gd_unit

Change-Id: Idcee5efd6eb6a62dad1d241496e489a696277af1