Collapse buttons if the row is too wide for the display

Prior to this, when resizing the dialogue to a sufficiently small size (such as happens on Plasma Mobile on the Pinephone), the row would overflow, resulting in a distinctly unpleasant look with a cut-off button. This patch fixes this by collapsing one of the buttons to icon-only, so there's space for all of them again (and then another, if there is even less space to work with).

Without this patch, the dialogue looks like this on PlaMo on a PinePhone:

With this patch (on a desktop, but the end result would be similar on a phone):