Allow for longer headlines

Constraint on headline length was too short for some languages.

Also need to ensure that longer strings work within the layout. Switched
to ConstraintLayout for that, with a Barrier to ensure that the modify
share and text toggle UI elements don't collide with the headline.

Test: Visual verification in a variety of configurations (diff share
      payloads, modify share action, etc)
Bug: 275755230
Change-Id: I2c2f1d9f9acaebd4f41d8d6f0791b58a26175100
2 files changed