EditorManager: Change openEditor/activateEditor to not do mode switching

Also introduce a indirection, modes have now types, edit and debug have
the same type, and editors do have a prefered type of modes instead of a
prefered mode.

That fixes the bug that if the prefered qml editing mode was set to
design, then in switching between qml editors would
- in Edit Mode: stay in edit mode
- in Debug Mode: switch to debug mode

src/plugins/coreplugin/mainwindow.cpp

@@ -964,7 +964,7 @@ void MainWindow::openFileWith()
         if (isExternal) {
             editorManager()->openExternalEditor(fileName, editorId);
         } else {
-            editorManager()->openEditor(fileName, editorId);
+            editorManager()->openEditor(fileName, editorId, Core::EditorManager::ModeSwitch);
         }
     }
 }
@@ -1272,7 +1272,7 @@ void MainWindow::openRecentFile()
     if (const QAction *action = qobject_cast<const QAction*>(sender())) {
         const QString fileName = action->data().toString();
         if (!fileName.isEmpty())
-            editorManager()->openEditor(fileName);
+            editorManager()->openEditor(fileName, QString(), Core::EditorManager::ModeSwitch);
     }
 }