Allow pressing a keybinding to select options in the confirmation dialogues

[00-kat]

This is not a duplicate as far as I know, though I did comment this on another tangentially related discussion (#4009) before.

It would be nice if something like y/n or alt+y/alt+n could be used to select one of the options in confirmation dialogues shown when closing a surface or pasting unsafe text. This is very common with popups in Qt applications and on Windows, though I don't think I've seen it much in GTK land though.

Note: I'm only asking for Linux and not macOS as I do not know what the convention is there.

Related to #2911.

[pluiedev]

I don't think this is idiomatic in GTK. Per the GNOME HIG, the only keybinds that should affect the dialog are:

• Tab/Ctrl-Tab which cycles between different dialog buttons
• Escape to cancel the action
• Enter to execute the action only if it's not destructive (close buttons count as destructive actions)

From what I can tell the alt+y/n shortcuts are actually using the mnenomics mechanism instead, like _Y_es and _N_o. I personally really dislike this design as underlines are ugly and mnemonics only make sense in English (other languages, for instance Chinese, require the mnemonic to be bracketed after the word, like 是(Y) — I consider this a crime against humanity)

I don't think it's physically possible to add a mnemonic to a dialog button either (at least when using AdwAlertDialog), which means implementing the event handling ourselves would be necessary — making all of this just a lot of work for little benefit IMHO.