https://bugs.webkit.org/show_bug.cgi?id=83047

Reviewed by Enrica Casucci.

Tests: platform/mac/editing/input/edit-dictated-text-with-alternative.html
       platform/mac/editing/input/insert-dictated-text.html

This patch implements visual indication on dictated text with alternatives, and provides UI
to show alternative text on OS X. Majority of the changes is for generalizing existing AlternativeTextController
class to handle dictation alternatives. The two new classes, AlternativeTextUIController and
TextAlternativeWithRange, are used by both WebKit and WK2. So WebCore seems to be the natural place
for them.

* WebCore.exp.in:
* WebCore.xcodeproj/project.pbxproj:
* editing/AlternativeTextController.cpp: Expanded exising class interface to support dictation alternatives.
(DictationAlternativeDetails): Marker detail class for dictation alternative mark.
(WebCore::DictationAlternativeDetails::create):
(WebCore::DictationAlternativeDetails::dictationCont...