QmlDesigner: Allow using assets from entire project in subfolders

If editing a subcomponent qml, assets tab now lists assets from the
entire project, and url/font choosers list appropriate resources
from entire project with correct relative paths.

Fixes: QDS-3638
Change-Id: I4a066c30d1bd696e8edbd17754bb9df2b7880873
Reviewed-by: Thomas Hartmann <thomas.hartmann@qt.io>
Reviewed-by: Mahmoud Badri <mahmoud.badri@qt.io>

src/plugins/qmldesigner/documentmanager.cpp

@@ -495,5 +495,12 @@ bool DocumentManager::belongsToQmakeProject()
     return proNode;
 }
 
+Utils::FilePath DocumentManager::currentResourcePath()
+{
+    Utils::FilePath resourcePath = currentProjectDirPath();
+    if (resourcePath.isEmpty())
+        return currentFilePath().absolutePath();
+    return resourcePath;
+}
 
 } // namespace QmlDesigner