Add configuration for disabling stylus button motion events

This adds an option for disabling stylus buttons from being reported as
part of a motion gesture. When disabled, all reported motion events'
button state will not include any stylus buttons. Key events are
unaffected.

This configuration is toggled through PhoneWindowManager based on
user-facing settings. Since this configuration does not affect KeyEvents
generated from stylus buttons, this gives a chance for the policy to
react to stylus button presses even when motion events are disabled.
For example, the policy can still be notified of stylus button presses
just as with any other key press, allowing the policy to make decisions
such as whether or not the device should be woken up. The policy can
also choose to ignore key presses and prevent them from being sent to
apps.

DD: go/android-stylus-buttons

Bug: 263256832
Test: atest inputflinger_tests
Change-Id: I68edaef5e6228aadf645586fbc1c4afcd499f712