Add support for adb scroll event injection

This enables simulating ACTION_SCROLL motion events. It supports sources
both of SOURCE_CLASS_POINTER and those that are not pointer-based.

Test: adb shell input scroll --axis SCROLL,-2 HSCROLL,3.2
Test: adb shell input scroll --axis BAD_AXIS,3 (fails, as expected)
Test: atest InputShellCommandTest
Bug: 298107774
Change-Id: If59cda07749344657155f6553fe0f15ef151f2e9