Closing a split editor tab, focus is not returned to the right tab

[liatbor]

Bug Description:

When closing an editor tab when we have split editors, the focus doesn't return to the tab that previously had the focus.

Steps to Reproduce:

1. Open a few files ( at least 3) so that multiple tabs are opened.
2. Drag and drop one of the tabs to create a split editor on the right
3. On the left side of the split screen, select one of the tabs that is not the right most tab
4. Close the editor tab on the right side of the split screen.
5. The focus is moved to the editor tab on the right ( instead of the one that was previously opened before)

Additional Information

• Theia Version: 1.19