Autoclick: Make click type buttons TalkBack accessible

The existing buttons have two issues when focused by TalkBack. They
announced themselves as images and they were not selectable using
"Search + Enter" once hovered.

To fix this, update each button by removing its LinearLayout wrapper and
only referencing the ImageButton.

Demo: http://b/427586021#comment2

Bug: 427586021
Test: AutoclickTypePanelTest
Flag: com.android.server.accessibility.enable_autoclick_indicator
Change-Id: I738b27b9eb711c721a46db9dc2b1eb1d0906cb3f