Inject Url Generator and Translator Interface into notification mailer

[askvortsov1]

Allows Fix For #1934

Allows us to get rid of https://github.com/flarum/mentions/blob/e054158ae5917d4edadb3c996e4c9ae992ab78e0/views/emails/postMentioned.blade.php#L5
moving one step closer to deprecating helpers

Changes proposed in this pull request:

• Inject an instance of translator into notification views
• Inject an instance of UrlGenerator into notification views

Reviewers should focus on:
What else should we inject? SettingsRepository came to mind, as well as possibly an optional associative array of arguments provided when calling $mailer->send One important thing to note is that we want to avoid an anti-pattern of business logic in the email views, so I'd stick to the essentials for now.

Confirmed

• Frontend changes: tested on a local Flarum installation.
• Backend changes: tests are green (run composer test).

[franzliedke]

@askvortsov1 Aren't these already available in views thanks to this?

https://github.com/flarum/core/blob/3b39c212e0fef7522e7d541a9214ff3817138d5d/src/Frontend/FrontendServiceProvider.php#L68-L71

[askvortsov1]

Isn't that only for page views / views returned as the result of the frontend?

[franzliedke]

If the mailer component uses the view component as well, it should be likewise affected.

[askvortsov1]

You are 100% correct. Sorry, I should have checked before implementing it. Reverted in 4ee6d6f

[franzliedke]

It was very easy to miss. Stumbled across those lines while changing something completely unrelated, just after having seen this PR a couple of hours earlier. 🤷

[askvortsov1]

Although I gotta say, does make me curious why these weren't translated in the first place...

[franzliedke]

Probably because it feels pointless to have a file only consisting of {{ trans() }} calls. There might have been thoughts about providing complete files in language packs. But as soon as HTML gets involved, that doesn't work well. 🤷 So I'm glad we're moving forward here.