applets/kicker: fix and simplify representation size

The horizontal sizing of the full representation is rather complex and due to circular dependencies somewhat buggy; in particular, searching for something that yields multiple results columns then clearing the search field will leave the menu column with the combined width of all the columns, rather than shrinking to its normal size.

We simplify this by having the optimal widths bubble up from the individual parts to the whole, rather than being circular in both directions. This also allows us to re-enable dynamic sizing for the (non-runner) full representation without the previous bugginess. (We keep the maximum width somewhat more limited at 1.5 times the normal width, as the menu is harder to operate when it is very wide, compared to the submenus or runner columns). Along the way, we use optional chaining to get rid of a runtime error that occasionally happens when closing Kicker.

BUG: 477005 FIXED-IN: 6.4.0