Remove translation change notification when setting the locale of a Translation resource

[YeldhamDev]

I've spend a hour trying to find the source of a bug in my code as to why NOTIFICATION_TRANSLATION_CHANGED was being triggered when I was not changing the game's locale. The cause? Apparently loading a Translation resource via code triggers the set_locale() method in it, triggering the notification.

While I get it why it triggers it when changing the locale of the whole game (via TranslationServer), triggering the notification by changing the locale of a resource doesn't make much sense to me.

[akien-mga]

It makes sense to me, NOTIFICATION_TRANSLATION_CHANGED doesn't only mean that the language changed, but it can mean that new translation resources have been loaded for the current locale and the scene's strings should thus be reloaded to take potential changes into account. (I did not look deep into it though so I might be missing something in this specific case.)

[YeldhamDev]

But the simple act of loading a translation resource (not adding it to the TranslationServer, just loading it) triggers it, and it's quite an annoyance when you have to load them at runtime.

[YeldhamDev]

I changed the commit to make the translation notification only emit if the resource is loaded in the TranslationServer. I don't see any other case where that would be useful otherwise.

[akien-mga]

The change makes sense to me, let's try to get @reduz to glance at it too to confirm that this was the intent for this notification. The documentation for NOTIFICATION_TRANSLATION_CHANGED in Node and MainLoop should likely also be clarified.

[YeldhamDev]

The documentation for NOTIFICATION_TRANSLATION_CHANGED in Node and MainLoop should likely also be clarified.

I'm quite sure nobody expects that to trigger when loading the resource itself to begin with.

[akien-mga]

Thanks!