Add support for custom highlight of ranges in textedit and textinput similar to QTextEdit::ExtraSelection

QML text input fields can currently only display either rich text or plain text. In many cases it's desirable to add a formatting to words or ranges, e.g. if you are using dictionaries or if you are showing pattern matches to a string or validation. This would mirror QTextEdit::setExtraSelections API;

http://doc.qt.nokia.com/latest/qtextedit.html#setExtraSelections