navigator: fix hidden toolbar icons when resizing

[vladarama]

What it does

This PR fixes #12602 by changing the styling of the explorer to make sure that the toolbar icons are always visible and that the folder name has an ellipsis overflow when the width of the Explorer is limited.

Demo:

How to test

• Open a folder with a long name
• Resize the Explorer view, reducing its width
• Toolbar icons should be visible and the folder name should have an ellipsis overflow

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]

The change looks good to me 👍

I'm not a big fan of the !important annotation, but it seems like that's an issue inherited from the perfect-scrollbar dependency and we cannot do a lot about that.

[vince-fugnitto]

LGTM 👍
Confirmed that toolbar items in headers have priority over the title which is a better user-experience.

[pisv]

I'm sorry for being late to the party, but I'd like to note that there has already been a pending PR for essentially the same issue: #12542. It is based on a slightly different approach and does not use the overflow: visible !important; style. Feel free to close it if is no longer relevant.