When 9.0.1856 was ported, the numbers being formatted as binary were cast
to "unsigned int" rather than uvarnumber_T, as is done upstream.

Since these assertions all use a common function to perform the test
assertions, it's difficult to figure out which test failed:

    ERROR    test/unit/testutil.lua @ 785: vim_snprintf() positional arguments
    test/unit/testutil.lua:757: test/unit/testutil.lua:741: (string) '
    test/unit/strings_spec.lua:143: Expected objects to be the same.
    Passed in:
    (number) 6400
    Expected:
    (number) 6'
    exit code: 256

Adding context to the assertion makes it clearer what the problem is:

    ERROR    test/unit/testutil.lua @ 785: vim_snprintf() positional arguments
    test/unit/testutil.lua:757: test/unit/testutil.lua:741: (string) '
    test/unit/strings_spec.lua:149: snprintf(buf, 0, "%1$0.*2$b", cdata<unsigned int>: 0xf78d0f38, cdata<int>: 0xf78dc4e0) = 001100
    Expected objects to be the same.
    Passed in:
    (number) 6400
    Expected:
    (number) 6'
    exit code: 256

Ref:
https://invisible-island.net/xterm/ctlseqs/ctlseqs.html#h3-Other-buttons

This commit adds basic support for the kitty keyboard protocol to
Neovim's builtin terminal. For now only the first mode ("Disambiguate
escape codes") is supported.

Problem:

Whether an option is allowed to be empty isn't well defined and
isn't properly checked.

Solution:

- For non-list string options, explicitly check the option value
  if it is empty.
- Annotate non-list string options that can accept an empty value.
  - Adjust command completion to ignore the empty value.
- Render values in Lua meta files

Also remove British National Replacement Character Set.

We keep the DEC Special Graphics and ASCII despite it not being unicode
as some old software such as calcurse still rely on this functionality.

References:
- https://github.com/neovim/neovim/pull/31934#discussion_r1911046426
- https://en.wikipedia.org/wiki/DEC_Special_Graphics
- https://vt100.net/docs/vt220-rm/chapter2.html#S2.4.3

Co-authored-by: Axel <axelhjq@gmail.com>
Co-authored-by: Colin Kennedy <colinvfx@gmail.com>
Co-authored-by: Daiki Noda <sys9kdr@users.noreply.github.com>
Co-authored-by: Evgeni Chasnovski <evgeni.chasnovski@gmail.com>
Co-authored-by: Jean-Jacq du Plessis <1030058+jj-du-plessis@users.noreply.github.com>
Co-authored-by: Juan Giordana <juangiordana@gmail.com>
Co-authored-by: Lincoln Wallace <locnnil0@gmail.com>
Co-authored-by: Matti Hellström <hellstrom@scm.com>
Co-authored-by: Steven Locorotondo <steven.locorotondo@justeattakeaway.com>
Co-authored-by: Yochem van Rosmalen <git@yochem.nl>
Co-authored-by: glepnir <glephunter@gmail.com>
Co-authored-by: ifish <fishioon@live.com>

We have changed too much to consider it a mere bundled dependency (such
as unicode handling in e3bfcf2fd4a4ebf00b104b082cfe83c8144a842d), and
can consider it our own at this point.