Navigator allows users to collapse workspace node

[caseyflynn-google]

Bug Description: Navigator allows users collapsing the workspace node

Theia allows the default workspace node to be collapsed which seems odd, and may be unintentionally invoked by users.

Steps to Reproduce:

1. Open the File Navigator view.
2. Ensure no file/directory is currently selected in the navigator (this may be accomplished by clicking the collapse all button)
3. Click an area in the File navigator that is not populated with a file
4. Press enter, or the left arrow key

Observe there are no files displayed.

Mitigation: After you are in this state, you may expand the workspace by pressing enter, or the right arrow, however this would not be apparent to a user who entered this state unintentionally.

Additional Information

• Operating System: Chrome OS / Linux:
• Theia Version: 1.6.0