a11y: Add autoclick indicator

When autoclick feature is enabled via settings, a visual indicator will
appear whenever the click event is about to fire. This aims to fill
the disparity between Android a11y and ChromeOS a11y.

Screen recording: http://go/scrcast/NTc5MDA2NzQ1MTc1NjU0NHw4MDQ1YmRmMS02OQ

Following work includes:
- Improve the look of the indicator
- Allow users to adjust the cursor area size
- Ignore minor cursor movement according to the cursor area size
- Allow reverting to left lick after action

Change-Id: Ifcc840bb24112f7751968c201c7caba810b68f44
Bug: b/383901288
Test: Verified locally
Flag: com.android.server.accessibility.enable_autoclick_indicator