QmlDesigner: Hide CollectionDetails when no collection is selected

Task-number: QDS-10621
Change-Id: Ifc5f16f4cffa1e0884394b94456da51505a18b2e
Reviewed-by: Mahmoud Badri <mahmoud.badri@qt.io>
Reviewed-by: Miikka Heikkinen <miikka.heikkinen@qt.io>
Reviewed-by: <github-actions-qt-creator@cristianadam.eu>

share/qtcreator/qmldesigner/collectionEditorQmlSource/CollectionDetailsView.qml

@@ -13,11 +13,16 @@ Rectangle {
 
     required property var model
 
+    implicitWidth: 600
+    implicitHeight: 400
+
     color: StudioTheme.Values.themeBackgroundColorAlternate
 
     ColumnLayout {
         id: topRow
 
+        visible: collectionNameText.text !== ""
+
         spacing: 0
         anchors {
             fill: parent
@@ -231,6 +236,17 @@ Rectangle {
         }
     }
 
+    Text {
+        anchors.fill: parent
+        text: qsTr("Select a collection to continue")
+        visible: !topRow.visible
+        textFormat: Text.RichText
+        color: StudioTheme.Values.themeTextColor
+        font.pixelSize: StudioTheme.Values.mediumFontSize
+        horizontalAlignment: Text.AlignHCenter
+        wrapMode: Text.WordWrap
+    }
+
     TextMetrics {
         id: headerTextMetrics