Problem:  A few remaining cmdline completion issues with C-E/Y
Solution: Fix cmdline completion fuzzy/Ctrl-E/Ctrl-Y/options when not
          used at the end

Fix cmdline completion fuzzy/Ctrl-E/Ctrl-Y/options when not used at the end

A few places in the cmdline completion code only works properly when the
user hits Tab (or 'wildchar') at the end of the cmdline, even though
it's supposed to work even in the middle of the line.

For fuzzy search, `:e ++ff`, and `:set hl=`, fix completion code to make
sure to use `xp_pattern_len` instead of assuming the entire `xp_pattern`
is the search pattern (since it contains texts after the cursor).

Fix Ctrl-E / Ctrl-Y to not jump to the end when canceling/accepting a
wildmenu completion. Also, make them work even when not using
`set wildoptions+=pum` as there is no drawback to doing so.
(Related issue where this was brought up: vim/vim#13331)

closes: vim/vim#13362

https://github.com/vim/vim/commit/209ec90b9b9bd948d76511c9cd2b17f47a97afe6

Cherry-pick ex_getln.c changes from patch 9.0.2035.

Co-authored-by: Yee Cheng Chin <ychin.git@gmail.com>

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.