Improve focus handling in Version Control pane

For example, after `git commit` (from locator) the focus is in the VCS pane, so you have to press ESC to get back to the editor. I think it would be enough here to open the VCS pane, but not to set the focus on it. Or only open the pane on error?

On the other hand, `git status` does not open the VCS pane if another pane is open. I even think, the pane should get focus here to be able to scroll around with the cursor keys. After all, the output is the only interesting thing from git status. Pressing ESC here one time should hurt no-one. If you don't like that, please consider adding an option.

See the previous discussion and my first attempt for a fix at https://codereview.qt-project.org/c/qt-creator/qt-creator/+/292955