Problem:  [security] use-after-free with wildmenu
Solution: properly clean up the wildmenu when exiting

Fix wildchar/wildmenu/pum memory corruption with special wildchar's

Currently, using `wildchar=<Esc>` or `wildchar=<C-\>` can lead to a
memory corruption if using wildmenu+pum, or wrong states if only using
wildmenu. This is due to the code only using one single place inside the
cmdline process loop to perform wild menu clean up (by checking
`end_wildmenu`) but there are other odd situations where the loop could
have exited and we need a post-loop clean up just to be sure. If the
clean up was not done you would have a stale popup menu referring to
invalid memory, or if not using popup menu, incorrect status line (if
`laststatus=0`).

For example, if you hit `<Esc>` two times when it's wildchar, there's a
hard-coded behavior to exit command-line as a failsafe for user, and if
you hit `<C-\><C-\><C-N>` it will also exit command-line, but the clean
up code would not have hit because of specialized `<C-\>` handling.

Fix Ctrl-E / Ctrl-Y to not cancel/accept wildmenu if they are also
used for 'wildchar'/'wildcharm'. Currently they don't behave properly,
and also have potentially memory unsafe behavior as the logic is
currently not accounting for this situation and try to do both.
(Previous patch that addressed this: vim/vim#11677)

Also, correctly document Escape key behavior (double-hit it to escape)
in wildchar docs as it's previously undocumented.

In addition, block known invalid chars to be set in `wildchar` option,
such as Ctrl-C and `<CR>`. This is just to make it clear to the user
they shouldn't be set, and is not required for this bug fix.

closes: vim/vim#13361

https://github.com/vim/vim/commit/8f4fb007e4d472b09ff6bed9ffa485e0c3093699

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

Problem:
NVIM_APPNAME does not allow path separators in the name, so relative
paths can't be used:

    NVIM_APPNAME="neovim-configs/first-config" nvim
    NVIM_APPNAME="neovim-configs/second-config" nvim

Solution:
Let NVIM_APPNAME be a relative path. Absolute paths are not supported.

fix #23056
fix #24966

Also avoid leaving directories behind.

Closes https://github.com/neovim/neovim/issues/23056.

Co-authored-by: zeertzjq <zeertzjq@outlook.com>
Co-authored-by: famiu <famiuhaque@protonmail.com>

Because E548 is linked to 'guicursor' in help.

Problem:    Vim9: builtin function arguments not checked at compile time.
Solution:   Add more type checks. (Yegappan Lakshmanan, closes vim/vim#8539)

https://github.com/vim/vim/commit/5b73992d8f82be7ac4b6f46c17f53ffb9640e5fa

Co-authored-by: Yegappan Lakshmanan <yegappan@yahoo.com>

test: replace lfs with luv

luv already pretty much does everything lfs does, so this duplication
of dependencies isn't needed.

Problem:
Using `meths.exec2("code", { output = true })` is too verbose.

Solution:
Use exec_capture() in more places.

Problem:
The signature of nvim_exec() is not extensible per ":help api-contract".

Solution:
Introduce nvim_exec2() and deprecate nvim_exec().