Stop adjustWidth from claiming cursor cells and styled spaces - #678

adjustWidth hides a following space so a standalone glyph can occupy
two cells, but never checked what that space was for. A box-drawing
border before an empty caret therefore stole the caret's cell and the
two rendered on top of each other.

followingCellProtected returns true when the following cell is the
cursor cell or belongs to a styled run; adjustWidth returns width 1 in
that case and leaves the space alone. An unused following space is
still claimed, so the original behaviour is intact everywhere else.

The fix is in Zig and MELPA ships only the Lisp, so it is carried as
patches/ghostel-v0.53.0-protect-cursor-spaces.patch against a
self-built module. init-local-shell.el points ghostel-module-directory
at ghostel-module/ only when a module is actually built there, and
otherwise leaves the variable unset so the stock module is used --
deleting the build is a complete rollback.

docs/ghostel-module.md records the exact Lisp/module pair, the Zig
0.16.0 build, the test command, and the removal criteria.

Submitted upstream as dakra/ghostel#678.

"Remove when upstream replaces it" named no ticket, so there was
nothing to watch and the patch would have become permanent by default.
Record dakra/ghostel#678 in the Pair list, beside the Lisp/module/patch
it belongs to, and in the removal criteria.

The criteria stay broader than the PR: upstream may close it in favour
of a different fix, and the patch should still come out in that case.

The docs change in 8003518 went in without a changelog line on the
grounds that be01168's entry already cited dakra/ghostel#678. Record
it explicitly instead, so the changelog carries the watch target rather
than leaving it implied by a neighbouring entry.