ui/ux: fix flickering icons when resizing explorer

[vladarama]

What it does

This PR closes #12615 by fixing the flickering of the toolbar icons when resizing the navigator. The issue was resolved by adding a new method called noPointerOnHover. This method temporarily disables pointer events on the explorer view when the mouse enters it which prevents the flickering behavior and leads to a better user experience.

Demo:

How to test

1. Open Theia application
2. Go in the Explorer view and open a folder if none are open (File -> Open Folder)
3. Click somewhere outside the Explorer view to make sure that it is not focused
4. Resize the view and notice that the toolbar icons stay hidden until you stop resizing the view

Review checklist

• As an author, I have thoroughly tested my changes and carefully followed the review guidelines

Reminder for reviewers

• As a reviewer, I agree to behave in accordance with the review guidelines

[msujew]

Thanks, looks good to me 👍