Fix flyspell-correct-word selected from context menu opened with the keyboard

Fix flyspell-correct-word selected from context menu opened with the keyboard

* lisp/mouse.el (context-menu-open): Call interactively a command
returned by `context-menu-map' such as `flyspell-correct-word' (bug#50067).

* lisp/textmodes/flyspell.el (flyspell-correct-word): Handle the
case when it's called by a key bound to `context-menu-open'.
Then it should work the same way as `C-c $' typed on misspelled word
where the arg `event' of `flyspell-correct-word-before-point' is nil.