Problem: No cmdline completion for the 'completefuzzycollect' option
(after v9.1.1178)
Solution: Add cmdline completion for the 'completefuzzycollect' option,
improve its description in optwin.vim (zeertzjq).
closes: vim/vim#1681353d59ecc1d
No code change is needed in Nvim as Nvim uses expand_set_str_generic()
by default.