Add "About / Help" menu item to the graphical interface

[MaurerAnton]

It would be nice to add an "About program / Help" menu item to the graphical interface.

I can start working on a pull request after I submit the PR I'm currently working on. I also noticed the existing tests aren't great and tried writing replacements for them.

If everything goes well, I'll send the current WIP tomorrow before sleep, then I can start on this feature. It'll probably take a couple of days to build and test. I have a bit of free time in the evenings each day.

[hiSandog]

The menu item will be easier to review if its scope is defined up front: application/version/build info, license/credits, documentation link, diagnostics, and update link are separate choices. Please keep the unrelated test rewrites out of this feature PR so behavior and coverage changes remain focused. A simple cross-platform UI test can verify the item opens and renders the current build metadata.