Model Visibility extender does not take into consideration missing
dependencies. For instance flarum/tags adds a policy on the Flag model
from flarum/flags. But because flarum/flags might as well not be
installed we need to check for the existence of that model. Otherwise
the exception is thrown or flarum fails to boot.
Since some boolean settings might be stored as string "0" or "1", the previous system no longer works, and it always sets the switch to true. The "no setting" check has been changed to reference `undefined`, so now the switch will only be defaulted to `true` if the setting truly hasn't been set.
Fixes https://github.com/flarum/core/issues/2574
Improves calculations for determining whether we are at the bottom of the notifications panel (which would trigger infinite scroll). This should be particularly effective in fixing issues on smaller screens.
We previously used the tobscure/m.attrs.bidi github repo, but that repo was recently taken offline. We decided to integrate it as a util instead of publishing it as a separate package since we seem to be the only project using it, and adopting it into a new project requires barneycarroll/mattr, which does not seem to be used anywhere.
The code added here was taken from https://github.com/askvortsov1/m.attrs.bidi, a fork (without changes) of the tobscure repo. Support for alternative module systems and ways of registering bidi were removed, and the file was formatted in compliance with our prettier config.
Historically, extensions using subscribers has caused problems because subscribers were constructed/applied at extension boot. This caused some classes (e.g. UrlGenerator) to be resolved early, breaking parts of Flarum. For this reason, subscriber support wasn't included in the initial version of the Event extender.
However, updating extensions has shown that there is a legitimate use case for subscribers in organizing clean code; for instance, core's own `DiscussionMetadataUpdater`.
This commit introduces support for subscribers, but only applies them after the app has booted, which avoids the early resolution issues. Since event listeners/subscribers are only intended to be used with domain events, which would never be dispatched during app boot, the late activation of subscribers should not cause issue.
