Add a readonly elided property to QML Text item

I would like to create a control where the text is elided by default, but if the text was shortened it shows an "expand" control that shows the full text.

There seems to be no way to tell if the display text in a Text item was shortened, either by the `elide` property or the `maximumLineCount`.

I thought maybe I could hack it using the `line.isLast` property in the `lineLaidOut` callback, but that seems to be set on the final visual line, not when the line is the actual last line in the text, so it doesn't work.

It would be very useful to have an `elided` property that would be `true` when the visible text was shortened by `elide` and/or `maximumLineCount`.