Prevent closing preference editor with the middle mouse click

Fixes #2639

- prevent closing preference editors using the middle mouse click by
setting the `title.closable` to `false`.

Signed-off-by: Vincent Fugnitto <vincent.fugnitto@ericsson.com>

packages/preferences/src/browser/preference-editor-widget.ts

@@ -56,6 +56,7 @@ export class PreferenceEditorTabHeaderRenderer extends TabBar.Renderer {
 
     renderTab(data: TabBar.IRenderData<PreferencesEditorWidget>): VirtualElement {
         const title = data.title;
+        title.closable = false;
         const key = this.createTabKey(data);
         const style = this.createTabStyle(data);
         const className = this.createTabClass(data);