QmlProject: Implement basic support for QmlFileSelector

This patch adds support for QmlFileSelector for
QmlProject and Qt Quick Designer.

Task-number: QDS-590
Change-Id: I0cc043d3ec9578008ec879b36fe834b70fb8c5ad
Reviewed-by: Ulf Hermann <ulf.hermann@qt.io>

src/plugins/qmlprojectmanager/qmlproject.cpp

@@ -225,6 +225,13 @@ QStringList QmlProject::customImportPaths() const
     return {};
 }
 
+QStringList QmlProject::customFileSelectors() const
+{
+    if (m_projectItem)
+        return m_projectItem.data()->fileSelectors();
+    return {};
+}
+
 bool QmlProject::addFiles(const QStringList &filePaths)
 {
     QStringList toAdd;
@@ -256,6 +263,13 @@ QStringList QmlProject::makeAbsolute(const Utils::FileName &path, const QStringL
     });
 }
 
+QVariant QmlProject::additionalData(Id id, const Target *) const
+{
+    if (id == Constants::customFileSelectorsData)
+        return customFileSelectors();
+    return {};
+}
+
 void QmlProject::refreshFiles(const QSet<QString> &/*added*/, const QSet<QString> &removed)
 {
     refresh(Files);