Dialog: support resizing of child widget

[Adam Peller]

Consider a preferences dialog which is a dijit.Dialog with a single BorderContainer widget in its contents. The BorderContainer must have a size, and the Dialog may resize itself to fit in the viewport, leaving the Dialog contents with a scrollbar. It should be possible to have the dialog resize the single child widget in this situation. I think this is related to the doLayout feature from ContentPane?

[bill]

It is related to doLayout, although a little different.

Normally the dialog's size is determined by it's contents; that's why doLayout is false. But in the special case where the dialog reduces the size of it's contents so the dialog itself fits in the viewport, it makes sense to do the resize of the single child widget like ContentPane does.

Actually this can already be tested with test_Dialog.html, with the TabContainer example.

[bill]

(In [19277]) When a Dialog's size needs to be reduced to fit in the viewport, and that Dialog contains a single layout widget, resize the layout widget, rather than adding a scrollbar to Dialog.containerNode.

Fixes #9588 !strict.

[bill]

(In [19278]) Remove "janktastic solution to #8967", which is no longer needed after [19277], since Lightbox doesn't even call Dialog._size(). Refs #8967, #9588 !strict.