a11y: Change selected button styling

Before: http://b/393548471#comment2
After: http://b/393548471#comment4

Notice the selected button has a highlighted color styling.

Change-Id: Iad1c06b7f592724aabb976938bb326ea7b851d30
Bug: http://b/393548471
Test: AutoclickTypePanelViewTest
Flag: com.android.server.accessibility.enable_autoclick_indicator