This new package provides an API that is easier to use right than
our `*-change-functions` hooks.

The patch includes changes to `diff-mode.el` and `eglot.el` to
make use of this new package.

* lisp/emacs-lisp/track-changes.el: New file.
* test/lisp/emacs-lisp/track-changes-tests.el: New file.
* doc/lispref/text.texi (Tracking changes): New subsection.

* lisp/progmodes/eglot.el: Require `track-changes`.
(eglot--virtual-pos-to-lsp-position): New function.
(eglot--track-changes): New var.
(eglot--managed-mode): Use `track-changes-register` i.s.o
`after/before-change-functions` when available.
(eglot--track-changes-signal): New function, partly extracted from
`eglot--after-change`.
(eglot--after-change): Use it.
(eglot--track-changes-fetch): New function.
(eglot--signal-textDocument/didChange): Use it.

* lisp/vc/diff-mode.el: Require `track-changes`.
Also require `easy-mmode` before the `eval-when-compile`s.
(diff-unhandled-changes): Delete variable.
(diff-after-change-function): Delete function.
(diff--track-changes-function): Rename from `diff-post-command-hook`
and adjust to new calling convention.
(diff--track-changes): New variable.
(diff--track-changes-signal): New function.
(diff-mode, diff-minor-mode): Use it with `track-changes-register`.

* lisp/vc/vc-hooks.el (vc-registered, vc-backend): Return nil
without invoking any backend if FILE or FILE-OR-LIST sits within
/content or /assets.

Remove extra "\n" from the end of the "diff --git.*" part
of 'diff-outline-regexp' because "\n" is not used in outline-regexp
and causes problems in such cases like when killing hunks
in the diff buffer with outline-minor-mode that loses
the outline icons because outline--fix-buttons-after-change and
outline--fix-up-all-buttons are limited to the single line and
can't match an outline line with a regexp that ends with "\n".

This re-applies:

  2024-03-17 "Fix vc-dir when "remote" Git branch is local"
  (21828f288ef)

reverted as part of the unrelated:

  2024-03-17 "Update modus-themes to their 4.4.0 version"
  (67b0c1c09ea)

The original commit message follows:

Fix vc-dir when "remote" Git branch is local

While in there, add that "tracking" branch to the vc-dir
buffer.  For bug#68183.

* lisp/vc/vc-git.el (vc-git-dir-extra-headers): Reduce
boilerplate with new function 'vc-git--out-ok'; stop calling
vc-git-repository-url when REMOTE is "." to avoid throwing an
error; display tracking branch; prefer "none (<details...>)" to
"not (<details...>)" since that reads more grammatically
correct.
(vc-git--out-ok): Add documentation.
(vc-git--out-str): New function to easily get the output from a
Git command.
* test/lisp/vc/vc-git-tests.el (vc-git-test--with-repo)
(vc-git-test--run): New helpers, defined to steer clear of
vc-git-- internal functions.
(vc-git-test-dir-track-local-branch): Check that vc-dir does
not crash.

* doc/misc/modus-themes.org: Update the manual to better document
existing functionality and cover the new features.

* etc/themes/modus-operandi-deuteranopia-theme.el:
* etc/themes/modus-operandi-theme.el:
* etc/themes/modus-operandi-tinted-theme.el:
* etc/themes/modus-operandi-tritanopia-theme.el:
* etc/themes/modus-vivendi-deuteranopia-theme.el:
* etc/themes/modus-vivendi-theme.el:
* etc/themes/modus-vivendi-tinted-theme.el:
* etc/themes/modus-vivendi-tritanopia-theme.el: Update the
palette of each theme.

* etc/themes/modus-themes.el (require): Remove call to cl-lib
and do not use relevant functions.
(modus-themes-operandi-colors, modus-themes-vivendi-colors)
(modus-themes-version, modus-themes-report-bug): Remove old
calls to 'make-obsolete' and related.

(modus-themes--annotate-theme): Tweak the completion annotation function.

(modus-themes--org-block): Deprecate the user option 'modus-themes-org-blocks'.
(modus-themes-faces): Update faces.
(modus-themes-custom-variables): Update the list of custom
variables.

Detailed release notes are available here:
<https://protesilaos.com/codelog/2024-03-17-modus-themes-4-4-0/>.

While in there, add that "tracking" branch to the vc-dir
buffer.  For bug#68183.

* lisp/vc/vc-git.el (vc-git-dir-extra-headers): Reduce
boilerplate with new function 'vc-git--out-ok'; stop calling
vc-git-repository-url when REMOTE is "." to avoid throwing an
error; display tracking branch; prefer "none (<details...>)" to
"not (<details...>)" since that reads more grammatically
correct.
(vc-git--out-ok): Add documentation.
(vc-git--out-str): New function to easily get the output from a
Git command.
* test/lisp/vc/vc-git-tests.el (vc-git-test--with-repo)
(vc-git-test--run): New helpers, defined to steer clear of
vc-git-- internal functions.
(vc-git-test-dir-track-local-branch): Check that vc-dir does
not crash.

It's bound to the recently added command 'diff-apply-buffer'.

There's no need to call 'get-buffer', since 'with-current-buffer'
does that internally.
* lisp/calendar/todo-mode.el (todo-merge-category):
* lisp/comint.el (comint-dynamic-list-completions):
* lisp/emacs-lisp/checkdoc.el (checkdoc-error):
* lisp/emacs-lisp/debug.el (debug, debugger-record-expression):
* lisp/emacs-lisp/eieio-opt.el (eieio-browse):
* lisp/emacs-lisp/re-builder.el (reb-restart-font-lock):
* lisp/erc/erc-dcc.el (erc-dcc-do-LIST-command):
* lisp/eshell/em-unix.el (eshell-poor-mans-grep):
* lisp/gnus/gnus-group.el (gnus-add-mark):
* lisp/net/eww.el (eww-next-bookmark, eww-previous-bookmark):
* lisp/net/sieve.el (sieve-upload):
* lisp/net/tramp-cmds.el (tramp-cleanup-some-buffers):
* lisp/obsolete/quickurl.el (quickurl-list-populate-buffer):
* lisp/org/ob-calc.el: (org-babel-execute:calc):
* lisp/org/org-agenda.el (org-agenda-use-sticky-p):
* lisp/pcomplete.el (pcomplete-show-completions):
* lisp/progmodes/bug-reference.el
(bug-reference--try-setup-gnus-article):
* lisp/progmodes/idlw-help.el
(idlwave-highlight-linked-completions):
* lisp/progmodes/verilog-mode.el (verilog-preprocess):
* lisp/replace.el (occur-1):
* lisp/term.el (term-dynamic-list-completions):
* lisp/time.el (world-clock-update):
* lisp/url/url-cache.el (url-store-in-cache):
* lisp/vc/vc-cvs.el (vc-cvs-merge, vc-cvs-merge-news):
* lisp/vc/vc-rcs.el (vc-rcs-system-release):
* lisp/vc/vc-svn.el (vc-svn-merge, vc-svn-merge-news):
* test/lisp/calendar/icalendar-tests.el
(icalendar-tests--get-error-string-for-export):
* test/lisp/erc/erc-dcc-tests.el
(pcomplete/erc-mode/DCC--get-1flag)
(pcomplete/erc-mode/DCC--get-2flags)
(pcomplete/erc-mode/DCC--get-2flags-reverse):
* test/lisp/erc/erc-networks-tests.el
(erc-networks--rename-server-buffer--existing--noreuse):
* test/lisp/erc/erc-scenarios-services-misc.el
(erc-scenarios-services-misc--reconnect-retry-nick):
* test/lisp/erc/erc-tests.el (erc--refresh-prompt):
Replace (with-current-buffer (get-buffer ...) ...) with
(with-current-buffer ...).