Provide `Text`'s text metrics

[Enyium]

Text should provide the actual metrics of its text. These new out-properties could be named text-x, text-y, text-width, and text-height.

With these, you can, e.g., implement a text background that isn't rendered too wide when text is wrapped. This SlintPad demo demonstrates the basic idea, although the background is still rendered too wide for wrapped text (change the preview size all the way from wide to narrow).

[tronical]

Wouldn't it perhaps make sense to generalise this? Elements have a geometry but they might render into a something slightly different. I'd call it the bounding rect, but there might be better terms out there.