Merge diff-font-lock-refine and diff-auto-refine-mode into diff-refine

This change was discussed in Bug#32991.

* admin/gitmerge.el (gitmerge-resolve): Bind 'diff-refine'
instead of 'diff-auto-refine-mode' to nil.
* doc/emacs/files.texi (Diff Mode): Explain 'diff-refine'
instead of 'diff-auto-refine-mode' in the documentation of
'diff-hunk-next' and 'diff-hunk-prev'.  Mention in the
documentation of 'diff-refine-hunk' that refining is already
done by default.
* etc/NEWS (Diff mode): Explain renamed 'diff-refine' variable
and mention deprecation and disabling of
'diff-auto-refine-mode'.
* lisp/vc/diff-mode.el (diff-font-lock-refine): Rename to
'diff-refine' and allow choices nil, 'font-lock' and 'navigation'.
(diff-auto-refine-mode): Disable it by default, make it
obsolete and make it set 'diff-refine' appropriately to keep
backward compatibility.
(diff-hunk-next, diff-hunk-prev): Adapt to rename of
diff-auto-refine-mode and ensure that refining only happens
when calling these commands interactively.
(diff--font-lock-refined): Adapt to rename of
diff-font-lock-refine.
* lisp/vc/smerge-mode.el (smerge-next, smerge-prev): Check
that 'diff-refine' is set instead of checking
'diff-auto-refine-mode' when deciding whether to refine a
conflict.
1 job for master in 51 minutes and 35 seconds (queued for 4 seconds)
Status Job ID Name Coverage
  Test
failed #957
test-all

00:51:35

 
Name Stage Failure
failed
test-all Test
Makefile:313: recipe for target 'check-doit' failed
make[2]: *** [check-doit] Error 1
make[2]: Leaving directory '/builds/emacs/emacs/test'
make[1]: *** [check-expensive] Error 2
Makefile:288: recipe for target 'check-expensive' failed
make[1]: Leaving directory '/builds/emacs/emacs/test'
Makefile:962: recipe for target 'check-expensive' failed
make: *** [check-expensive] Error 2
ERROR: Job failed: exit code 1