WelcomeScreen: QImageProvider fix

Adapting to fix for QTBUG-38127. Otherwise, the icons are too big in a
HighDPI case.

Task-number: QTBUG-38127
Change-Id: I70e27c06eaf1f2efa89c31d0a190aba52af28038
Reviewed-by: Eike Ziller <eike.ziller@theqtcompany.com>

share/qtcreator/welcomescreen/widgets/ProjectItem.qml

@@ -41,6 +41,8 @@ Rectangle {
         id: icon
         x: 11
         y: 6
+        height: 16
+        width: 16
         source: "image://icons/project/Welcome_ForegroundSecondaryColor"
     }
 

share/qtcreator/welcomescreen/widgets/SessionItem.qml

@@ -49,6 +49,8 @@ Item {
                 source: "image://icons/session/Welcome_ForegroundSecondaryColor"
                 x: 11
                 anchors.verticalCenter: parent.verticalCenter
+                height: 16
+                width: 16
             }
 
             NativeText {
@@ -196,6 +198,8 @@ Item {
                 visible: (collapseArea.containsMouse || delegate.expanded || titleArea.containsMouse)
                 source: "image://icons/expandarrow/Welcome_ForegroundSecondaryColor"
                 rotation: delegate.expanded ? 180 : 0
+                height: 16
+                width: 16
             }
         }