applets/notifications: set implicit size

Without this, the FullRepresentation opens to an unusably small size
when it's a Panel applet.

BUG: 448383
FIXED-IN: 5.24


(cherry picked from commit 9a6b190046)

applets/notifications/package/contents/ui/FullRepresentation.qml

@@ -24,6 +24,10 @@ PlasmaExtras.Representation {
     // TODO these should be configurable in the future
     readonly property int dndMorningHour: 6
     readonly property int dndEveningHour: 20
+
+    implicitWidth: PlasmaCore.Units.gridUnit * 16
+    implicitHeight: PlasmaCore.Units.gridUnit * 16
+
     Layout.fillHeight: plasmoid.formFactor === PlasmaCore.Types.Vertical
 
     collapseMarginsHint: true