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/cpptools/cppfindreferences.cpp

@@ -304,9 +304,11 @@ void CppFindReferences::searchFinished()
 void CppFindReferences::openEditor(const Find::SearchResultItem &item)
 {
     if (item.path.size() > 0) {
-        TextEditor::BaseTextEditor::openEditorAt(item.path.first(), item.lineNumber, item.textMarkPos);
+        TextEditor::BaseTextEditor::openEditorAt(item.path.first(), item.lineNumber, item.textMarkPos,
+                                                 QString(),
+                                                 Core::EditorManager::ModeSwitch);
     } else {
-        Core::EditorManager::instance()->openEditor(item.text);
+        Core::EditorManager::instance()->openEditor(item.text, QString(), Core::EditorManager::ModeSwitch);
     }
 }