Qt Quick: Separate Qt Quick Designer and QMLJS editor factories

Currently the QmlJSEditorFactory hardcodes that .qml.ui files are opened
"in Design mode", without any option to explicitly open them directly in
text mode.
While this is the preferred way of working, there are always exceptions.

Separate the "Edit mode by default" and the "Design mode by default"
parts into separate editor factories. The former one is the default
editor for .qml files, the latter for .qml.ui files.

This allows users to explicitly choose "Open With > QML JS Editor" to
open .qml.ui files directly in Edit mode.

Fixes: QTCREATORBUG-18123
Change-Id: I72ab2d25fdc538210123782f6611f9c6e3157dea
Reviewed-by: Christian Stenger <christian.stenger@qt.io>
Reviewed-by: Thomas Hartmann <thomas.hartmann@qt.io>

src/plugins/qmljseditor/qmljseditor.h

@@ -136,6 +136,7 @@ class QMLJSEDITOR_EXPORT QmlJSEditor : public TextEditor::BaseTextEditor
 public:
     QmlJSEditor();
 
+    QmlJSEditorDocument *qmlJSDocument() const;
     bool isDesignModePreferred() const override;
 };
 
@@ -145,6 +146,7 @@ class QMLJSEDITOR_EXPORT QmlJSEditorFactory : public TextEditor::TextEditorFacto
 
 public:
     QmlJSEditorFactory();
+    QmlJSEditorFactory(Core::Id id);
 
     static void decorateEditor(TextEditor::TextEditorWidget *editor);
 };