Pass through 'helpInline' to OOUI FieldLayout and make true by default
This change is meant to improve the layout of Special:Preferences in
particular, but it will affect any OOUI form using help messages. It
should be a harmless or beneficial change for most of them.
Previous behavior can be restored by passing `'help-inline' => false`
to the HTMLForm factory after 'help-message'/'help-messages'/'help'.
For example:
* Special:Preferences?ooui=1#mw-prefsection-watchlist
* Before: https://phabricator.wikimedia.org/
F25025213
* After: https://phabricator.wikimedia.org/
F25025181
* Special:ChangeEmail
* Before: https://phabricator.wikimedia.org/
F25073327
* After: https://phabricator.wikimedia.org/
F25073328
* Special:BotPasswords/foo
* Before: https://phabricator.wikimedia.org/
F25073324
* After: https://phabricator.wikimedia.org/
F25073326
Bug: T181854
Change-Id: Ica67fe4081dfaa8eb9e8f56fdb93530750e47012