Fixes #211: Add Autosuggest/TextReplacement

This commit is a promotion of the internal TextReplacement API. The
TextDecorator was nehanced to allow setting a TextReplacementData on a
Text widget. Also some minor renaming was done to finalize the API.

Change-Id: Iab8588e5e4713bebbe7bc8b4b7898b81956db98f