Focused Editor Context Not Updated When New Editor Focused

[colin-grant-work]

Bug Description:

EditorWidget has a handler for onSelectionChanged that updates the global selection to the current editor. However, that code does not fire if the user switches editors without moving the cursor in the new editor.

Steps to Reproduce:

(see #9013)

1. Clone https://github.com/avishaik/vscode-editor-btn-bug

2. update the when statement in the package.json in contributes -> menus -> editor/title to:
   "resource =~ /^(.)/pages/(.)$/ && editorLangId == json && editorFocus == true"

3. Build it: npm run package and add it as extension to Theia

4. Create a .json file on the root folder

5. Create a 'pages' folder and create another .json file in this folder

6. Open both files side by side

7. Move the cursror in the JSON file.

8. Observe that the icon appears for the JSON file.

9. Activate the markdown editor without moving the cursor.

10. Observe that the icon still appears

Additional Information

• Operating System: RHEL
• Theia Version: master (2/8/2021)