Fix insertion handle disappearing in extract mode

In extract mode, on every screen touch
TextView#setExtractedText gets called which calls
SpannableStringBuilder#sendTextChanged which in turn stops
the action mode. As a fix, if the text is the same only
copy the spans without replacing everything.

Bug: 22315095
Change-Id: I28da760b3dc11e1cfbaf720e547bd817c5b89d7e