Can't easily open PR to the right

[joaomoreno]

Testing #8536

With files I can easily:

1. Open a file
2. View: Split Editor
3. Open another file

And I'll end up with two files side by side.

I can't seem to do this with PRs. I think the main reason is that the View: Split Editor isn't working for PRs, it just creates an empty editor group. I can see why we wouldn't want Split Editor to work (we only want one editor per PR). Still the question remains: if the empty editor group is focused, why isn't the PR I click opening there? That works in regular files.

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Also, from the File Explorer I can Alt click a file to open it to the side. That also doesn't seem to work from the PR view.