[Calendar] Shrink and elide week names like is done with day delegate

This ensures week names never exceed their cell's boundaries.

BUG: 378020

Differential Revision: https://phabricator.kde.org/D5200

src/declarativeimports/calendar/qml/DaysCalendar.qml

@@ -317,6 +317,8 @@ Item {
                 opacity: 0.4
                 horizontalAlignment: Text.AlignHCenter
                 verticalAlignment: Text.AlignVCenter
+                elide: Text.ElideRight
+                fontSizeMode: Text.HorizontalFit
             }
         }