Improve paging hint

[crzcrz]

This PR attempts to improve the paging hint displayed when all key bindings do not fit on the screen.

• Avoid suggesting C-h when it will certainly not work,
• Suggest alternatives that were previously not offered (? and <f1>),
• Suggest custom bindings to 'which-key-C-h-dispatch (when present).

This should improve the experience for newcomers a bit.

Tested under clean Emacs 29.3 and Doom v3.0.0-pre from yesterday.

When testing today I've noticed that C-h C-h now works under Doom and displays the paging prompt, while it certainly did not when I submitted #368, and it still does not in "clean" Emacs. However in the original implementation we would not display any paging hint at all, so I don't think we are making anything worse.

Closes #368

[justbur]

Thanks. Sorry for not asking earlier, but have you assigned your copyright to the FSF (see here)?

[crzcrz]

It’s in progress.

[justbur]

Hi @crzcrz, I'm not sure what the status is on this, but I'm planning to archive this repo as which-key was recently merged into the master branch of emacs. Contributions can now be considered through the standard emacs channels.