Allow to switch From <> To diff direction

[themilkman]

Problem description

When comparing two selected commits, it is currently not possible to switch the diff direction (diff A B vs diff B A).

Preferred solution

Add command palette entry to switch the direction of the current diff. There might be smarter ways to do this regarding UX, but that'd already be helpful.

Alternatives

Respect the order of the selected commits on clicking. Not sure how to smart handle multiple selections then, maybe take the first always as base.