Focus briefly disappears from editor when clicking in sidebar

[peterflynn]

1. Enable Active Line Highlight or drag out a selection, so it's more obvious when the editor doesn't have focus
2. Click in the working set or project tree to select a different file
3. Click the same file that is already selected

Result:
Step 2 - selection briefly disappears from the editor before the next file is selected
Step 3 - selection briefly disappears from the editor and then is restored

This is a regression new in 0.44 -- not sure if two separate issues in the tree vs. working set, or the same cause for both (it is two different causes).

[peterflynn]

Now that #9433 has landed, this only reproduces for the file tree.