Add EditTextShortcutSpan to provide edit short cut in the text view.

At the moment, EditTextShortcutSpan allows only the deletion of the text. In the future, we may decide to add extra functionality,
like "retry" where all the text is removed and a specific IME is triggered.

Fix the underline. The underline is not defined in thickness, and not as a multiplier of the default underline thickness.

Change the behaviour of SuggestionRangeSpan to match the specification.

Change-Id: I80437d9887c7a2ff8f62c38afbb0cb7add7ee9c8