Extracted text problems

Bug 5557258: recent text editing changed in ExtractedText mode is
broken. The modifications of the text performed by:
- drag and drop
- text suggestions, deletion
- voice IME's delete button

all change the ExtractEditText itself, while they should affect the underlying
EditText (and the change will be forwarded to the ExtractEditText). As a results,
changes are not actually modifying the underlying text.

Created new protected methods in TextView, overloaded in ExtractTextView to
affect the underlying text instead.

Changes to spans should also be forwarded to the original TV (see the 2 TODOs),
this is tracked in bug 5589158.

Change-Id: Ibfec272469e8db191b3875e7576e32481a9dc1bd