Improve doc of `mouse-drag-mode-line-buffer'

* doc/emacs/frames.texi (Mouse Commands): Document
`mouse-drag-mode-line-buffer'.
* etc/NEWS: Explain where that option is supported.
* lisp/mouse.el (mouse-drag-mode-line-buffer): Likewise.
1 job for master in 1 minute and 12 seconds (queued for 5 seconds)
Status Job ID Name Coverage
  Normal
failed #46767
test-lisp-inotify

00:01:12

 
Name Stage Failure
failed
test-lisp-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
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WARNING: test-lisp-inotify-eaff6569/: no matching files
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Uploading artifacts...
WARNING: test-lisp-inotify-eaff6569/junit-test-report.xml: no matching files
ERROR: No files to upload
ERROR: Job failed: exit code 128