Add "dictionary" entity type

We will classify the word as "dictionary" if we think user may want to look
it up. A "Dictionary" option will be shown in the floating toolbar
if users select words of this entity type.

A new Intent action is introduced to bring up the dictionary app.

The model that supports this entity type is not checked-in yet.
So no behavior change can be seen for now.

Test: Check-in the WIP model and try to select a "dictionary word".
Test: atest frameworks/base/core/tests/coretests/src/android/view/textclassifier/IntentFactoryTest.java

BUG: 68238822

Change-Id: Ib318d5b2abf79d61e55b33e397065a0714573121