Read DIS info for Fast Pair Devices

Schedule DIS model name read before service discovery is scheduled.
Also move it to BTIF layer, which is more proper than gatt_main.cc

Bug: 337087330
Bug: 322464947
Test: pair using Fast Pair with LE Audio capable device
Flag: com.android.bluetooth.flags.read_model_num_fix
Change-Id: I7df16768f49f18c1e76c1722ef39075dd43bf37d