a11y: Throttle motion events for magnification UI update

This change introduces a throttling mechanism for motion events
to prevent excessive UI updates in magnification.

Previously, only mouse events were throttled, leading to potential
performance issues with touch events. This change extends the
throttling to touch events as well, guarded by a feature flag
`throttle_motion_events_for_ui_update`.

The following tests have been added to ensure the throttling works
as expected with and without the feature flag:
- onTouchEvent_withThrottleEnabled_shouldRateLimit
- onTouchEvent_withThrottleEnabled_shouldNotRateLimitAfterDelay
- onTouchEvent_withThrottleDisabled_shouldNotRateLimit

Bug: 435498747
Flag: com.android.server.accessibility.throttle_motion_events_for_ui_update
Test: atest MagnificationControllerTest
Change-Id: I2283d944ab30c6eed4f03d56d42afac8c6ec33c2