wifi(interface): Add gscan/apf related API's

Changes in the CL:
1. Add gscan/APF related API's to |IWifiStaIface|.
2. Add a new callback HIDL interface (|IWifiStaIfaceEventCallback)
for all callbacks received from |IWifiStaIface|.

Bug: 31991459
Test: Compiles
Change-Id: Id9f2ded9e20bee393ab53d84efa814d52704cd2c