Introduce full justification.

Adds a new get/setJustify API to TextView and StaticLayout.Builder for
justification, and fully justifies text when it's enabled.

This is based on a patch by Raph Levien (raph@google.com).

Bug: 31707212
Test: Manually done and CTS will introduced with
      I0f3bbf39d60a66b71b30e1351f7c741208f05dce passes.
Change-Id: Icbfab2faa11a6a0b52e6f0a77a9c9b5ef6e191da