Problem:    Command line popup menu not positioned correctly.
Solution:   Also use vim_strsize() on the existing text. (Naruhiko Nishino,
            closes vim/vim#9727)
https://github.com/vim/vim/commit/68cc2b8a37197872e737fb61244069e13b7227a2

Problem:    'wildmenu' only shows few matches.
Solution:   Add the "pum" option: use a popup menu to show the matches.
            (Yegappan Lakshmanan et al., closes vim/vim#9707)
https://github.com/vim/vim/commit/3908ef5017a6b4425727013588f72cc7343199b9

Omit p_wmnu check in cmdline_pum_active() as it can cause problems.
Omit vim_strchr() flags as that isn't really better than bitmasks.
Omit key translations and document it in vim_diff.txt.