Providing new accessibilityNode action

Providing a new A11yNode action for ime actions:
ACTION_IME_ENTER
1. TextView will expose this action and store the ime action id
if it is editable and has focus.
2. This A11y action which would have default text “Enter” if the
developer didn’t set a custom ime action label, otherwise the label
would be what the developer provided.
3. This A11y action which would have default id,
IME_ACTION_UNSPECIFIED if the developer didn't set a custom ime
action id, otherwise the id would be what the developer provided.
4. TextView will perform this action by calling its onEditorAction
with stored ime action when populating this node.

Bug: 139380257
Test: a11y CTS tests & unit tests
Change-Id: Ifba432f8fda732f8335c40fe27f5e74499621d47