[austinderrick]

Moves the change from wintercms/winter#1511 into this plugin, so core needs no Octane-specific check.

Winter's System, Backend and Cms providers register back-end navigation, widgets and settings only for back-end requests. A worker registers its providers once, against a request that is not a back-end request, so a worker served every back-end page with empty menus and settings. The plugin now makes those registrations itself in a worker. It runs them from a booting callback, after every provider has registered and before any provider or plugin boots, so core's callbacks run in the same order as under PHP-FPM. Outside a worker it does nothing.

Also:

• CI runs against wintercms/winter and wintercms/storm wip/1.3 instead of the #1511 fork branches.
• The README tells plugin authors not to put registrations behind App::runningInBackend(), because a worker never registers anything behind that check.

Testing

OctaneRegistrationTest checks that the registrations are made in a worker and not outside one. The suite (44 tests), phpcs and PHPStan pass against Winter wip/1.3. A cold boot through Octane's ApplicationFactory with the client bound registers 3 navigation, 3 settings and 2 form widget callbacks, and none without it.