revealWidget provides no visual feedback if widget already visible

[colin-grant-work]

Bug Description:

If you click on a file node in the navigator, that file is opened in an editor preview and then it is 'revealed' (but not focused) using the shell.revealWidget. If that widget is still visible and you later click on the file node, nothing happens. In VSCode, the title is changed to the active color, though focus is not transferred to the widget.

Steps to Reproduce:

1. Set editor.enablePreview preference set to true (default).
2. Single-click on a file node in the navigator.
3. Observe that the file is opened but not focused and the title has 'inactive' coloring (grey-ish). In VSCode, it would have 'active' coloring (brighter white or black).
4. Focus another widget but keep that editor visible.
5. Observe that in Theia, the color of the title doesn't change, but in VSCode it transitions to 'inactive' coloring.
6. Click the same file node in the navigator. Observe that in Theia, nothing changes, but in VSCode the editor title gets 'active' coloring again.

Additional Information

• Operating System: RHEL7
• Theia Version: 1.14.0