Introduce Translate intent.

Action: ACTION_TRANSLATE
Text: EXTRA_TEXT

TODO: Consider introducing a "translate" schema to pass the text to
translate instead of using a string extra to define this.

Bug: 116020587
Test: manually tested by selecting foreign language text and watching
      for a "Translate" action.
Change-Id: I046157f4b3e1aa60afaf3f123fdeecf406f712dc