Refactor and clean up USB, add tests

Change UsbManager apis to use long instead of string, to match
usb hal. Change UsbDeviceManager internals to match as well.

Remove isFunctionEnabled and add getEnabledFunctions. Callers
would often call isFunctionEnabled for every possible function
to get the list of functions, so getEnabledFunctions reduces the
number of aidl calls.

Separate out dependencies between UsbHandler and UsbDeviceManager
and staticize the UsbHandler classes. Add unit tests with
mocked out dependencies to test state transitions for UsbHandler.

Bug: 62876645
Test: atest UsbTests
Change-Id: I785c4c24121a70e725de9742c6af50a6bf1baea0