Currently, if you right-click the desktop and then click somewhere
else(e.g. panel), the popup will stay visible.

This happens because KWin doesn't dismiss popups if you click somewhere
else in the same app. The desktop window and the panel window belong to
the same app so the popup is not dismissed.

From user's perspective this is wrong because the popup lost focus, thus
it should be dismissed.

testDecoCancelsPopup was deleted because it doesn't really matter
whether we click window decoration, what matters is whether we click outside
of popup.

BUG: 379635
FIXED-IN: 5.14.0

• Right-clicked desktop, then clicked panel (the popup disappeared);
• Right-clicked empty area in Dolphin, then clicked the "Control" button (the popup disappeared);
• Right-clicked empty area in Dolphin, then clicked empty area on my desktop (the popup disappeared).