Add util method to check if MotionEvent is synthesized touchpad gesture

This check is being done in many places:
- WMShell MotionEvent extensions
- Settings DisplayTopologyPreferenceController
- MouseToTouchProcessor
- A11y

More might be added in the future. Ideally having this unified under
MotionEvent itself might be better, similar to isTouchEvent() or
isStylusPointer() check. If there's a new classification or new
condition in the future, it can be added here and all usages are updated

Bug: 436380669
Test: Manual test with touchpad
Flag: EXEMPT adding hidden util method
Change-Id: I2f8384ffa807a9516ba9dedfdee3e0d31caddda0