Dialog does not correctly compute children width

[Benjamin Zeller]

The Dialog popup does not correctly compute the width of its children elements,
resulting in long text being clipped, even if enough space is available to expand the Dialog itself.

If not enough space is available, text could also be wrapped or elided, maybe controlled with a attribute.

The ItemSelector item in the attached example, shows the problem.

[Cris Dywan (kalikiana)]

So there's three related issues here:

1. Dialog ignores implicitWidth
2. Components don't implement implicitWidth
3. All *Selector components don't ellide

The attached branch addresses the first one, which also enables applications to work ar

[Cris Dywan (kalikiana)]

ound the issue by setting implicitWidth on components that don't implement it.