a11y: Support auto right-click

Demo: http://b/388844954#comment2. Notice that right clicking opens the
context menu.

Change-Id: Ic970ff90d61de21310370b442d6f881627ed531b
Bug: b/388844954
Test: AutoclickControllerTest, AutoclickTypePanelTest
Flag: com.android.server.accessibility.enable_autoclick_indicator