Consider showing "Alt" instead of "Command" for PC keyboards

Was considering showing "Alt" instead of "Command" for PC keyboards, but wasn't sure whether it would further complicate things (think screenshots and documentation).

Now it has been asked on Twitter:
https://twitter.com/mister_lemke/status/1449008251622748163

Let's think about the best way to go about this.

Start by reviewing the current QKeySequenceOverride behavior and how shortcut labels are produced for different keyboards. Clarify whether PC keyboards should display "Alt" instead of "Command", then define the expected behavior and account for the stated screenshots and documentation concerns.

Vom Indexierungsmodell aus dem Issue-Text verfasst.