Add Alt-F shortcut for opening menu in the top-right

[zhouyc98]

I think adding "Alt-F" shortcut to open the menu in the top-right is a good idea. Many apps use this shortcut like chrome and edge browser :)
Currently, opening the menu is linked with a hotkey "`", but it is not intuitive and not easy to be pressed compared to Alt-F.

[d2phap]

Yea, it's changed to Alt+F in the latest build of IG Moon: https://imageglass.org/moon, also mentioned here:
#970 (comment)