floss: Revise UUID update logic for scan result and device found

2 issues are addressed here:
- OnDevicePropertiesChanged is not fired for DeviceFound while it should
  be expected per the btif_dm implementation
- The existing UUIDs were entirely replaced by them which is just wrong

Bug: 354783606
Bug: 345382885
Tag: #floss
Test: mmm packages/modules/Bluetooth
Flag: EXEMPT, Floss-only changes
Change-Id: If098bcc8a055c0c67157f0d015736e5d17448680