Reconvert EPUB buffers when user CSS is changed

* lisp/doc-view.el (doc-view-epub-user-stylesheet): Add
`doc-view-custom-set-mutool-user-stylesheet' as setter, change name.
(doc-view-custom-set-epub-font-size): Factor reconvert logic out
(doc-view--epub-reconvert): Add defun
(doc-view--epub-stylesheet-watcher): Add defvar
(doc-view-custom-set-epub-user-stylesheet): Add defun (bug#55825).
10 jobs for master in 258 minutes and 27 seconds (queued for 19 seconds)
Status Job ID Name Coverage
  Build Images
passed #48275
build-image-inotify

01:37:40

 
  Normal
failed #48276
test-all-inotify

00:37:31

 
  Platform Images
passed #48277
build-image-filenotify-gio

01:37:36

passed #48278
build-image-gnustep

00:40:04

 
  Platforms
passed #48279
test-filenotify-gio

00:15:55

passed #48280
test-gnustep

00:06:55

 
  Native Comp Images
passed #48281
build-native-comp-speed0

03:45:32

passed #48282
build-native-comp-speed1

00:45:48

passed #48283
build-native-comp-speed2

02:30:38

 
  Native Comp
passed #48284
test-native-comp-speed0

00:32:50

 
Name Stage Failure
failed
test-all-inotify Normal
$ find ${test_name} ! \( -name "*.log" -o -name ${EMACS_TEST_JUNIT_REPORT} \) -type f -delete
$ find ${test_name} -type d -depth -exec rmdir {} + 2>/dev/null
Uploading artifacts...
test-all-inotify-51f24fe2/: found 442 matching files
Uploading artifacts to coordinator... ok
id=48276 responseStatus=201 Created token=pbvT3Euz
Uploading artifacts...
test-all-inotify-51f24fe2/junit-test-report.xml: found 1 matching files

Uploading artifacts to coordinator... ok
id=48276 responseStatus=201 Created token=pbvT3Euz
ERROR: Job failed: exit code 2