QmlDesigner: Add new way to load fonts to template

StudioApplication will load the correct font in time.
This only works for Qt 6.

Task-number: QDS-3286
Change-Id: I2d97ca19bace8e13c7a4df355d1addb7267e117c
Reviewed-by: Tim Jenssen <tim.jenssen@qt.io>
(cherry picked from commit 099f02b5db)

share/qtcreator/qmldesigner/studio_templates/projects/shared-plugin/name/Constants.qml.tpl

@@ -1,12 +1,15 @@
 pragma Singleton
 import QtQuick %{QtQuickVersion}
+@if %{IsQt6Project}
+import QtQuick.Studio.Application
+@else
+@endif
 
 QtObject {
     readonly property int width: %{ScreenWidth}
     readonly property int height: %{ScreenHeight}
 
-    property alias fontDirectory: directoryFontLoader.fontDirectory
-    property alias relativeFontDirectory: directoryFontLoader.relativeFontDirectory
+    property string relativeFontDirectory: "fonts"
 
     /* Edit this comment to add your custom font */
     readonly property font font: Qt.font({
@@ -20,7 +23,14 @@ QtObject {
 
     readonly property color backgroundColor: "#c2c2c2"
 
+
+@if %{IsQt6Project}
+    property StudioApplication application: StudioApplication {
+        fontPath: Qt.resolvedUrl("../../content/" + relativeFontDirectory)
+    }
+@else
     property DirectoryFontLoader directoryFontLoader: DirectoryFontLoader {
         id: directoryFontLoader
     }
+@endif
 }