dispatch: sort the loaded extension names in the bug report
This makes a long list of extensions easier to read. On very rare occasion I've
seen issues where the load order mattered, however that info should still be
obtainable with `hg config extensions`.
Differential Revision: https://phab.mercurial-scm.org/D9439
#require docutils gettext
$ $TESTDIR/check-gendoc sv
checking for parse errors