Migrate IUsbGadget to AIDL

This change migrates android.hardware.usb.IUsbGadget to AIDL and
adds the default implementation.

Compared to the HIDL interface, AIDL based interface adds
transactionId argument to each of the interface method which
is used while invoking the corresponding callback.

Bug: 218791946
Test: USB function switch success and AIDL service is running.

Signed-off-by: Ricky Niu <rickyniu@google.com>
Change-Id: Ie05354660f13c8047e2c1712bf373e8699874d28