Implement ACTION_LONG_CLICK for accessibility

Due to changes in R, the a11y framework no longer dispatches touch
events for a long press. This prevents the activation of EditText's floating menu.

We can re-enable it by implementing the proper a11y action
ACTION_LONG_CLICK. The menu itself is diffult to access through TalkBack's linear
navigation, but this is future work for a separate known issue.

Start and stop the menu for editable TextViews, which includes EditTexts.
Since touch events are no longer sent by a11y, separate the
accessibility handling from the touch handling infrastructure for long clicks in Editor.

We can't go through the main performLongClick code because it doesn't
actually start the action mode but rather sets pending, which routes
back to TextView. There's too little separation between the touch events and action logic.

Whoever touches the performLongClick code may need to also make
corresponding changes to the a11y path, but I suspect this won't happen often.

Remove the onInitializeA11yNodeInfo override for EditText because this
is handled by TextView.

Bug: 148127445
Test: Tested text fields in various apps. ag/10602004. atest
FrameworksCoreTests:TextViewActivityTest#testToolbarAppearsAccessibilityLongClick

Change-Id: I3958e5b80e6156e03c99335e0d0b671438965ebb
(cherry picked from commit 3f1203fb)
Merged-In: I3958e5b80e6156e03c99335e0d0b671438965ebb