Improvement of IME Enter Action

1. Remove the internal using argument, ACTION_ARGUMENT_IME_ACTION_ID_INT.
2. Add more descriptions about this accessibility action, ACTION_IME_ENTER

Bug: 150831470
Test: atest AccessibilityTextActionTest
Change-Id: Icfebdf280e3441bf7b2b6f55c3febbe3a1d98de6