Consider applying core mixins to WidgetBase by default

[agubler]

Enhancement

The main core mixins, Themeable, I18n and Registry provide functionality that could be automatically mixed in to WidgetBase by default. This would remove possible friction for consumer to need to deal with the mixin concept early on in Dojo 2 adoption.

The mixins are all additive functionality and shouldn't impact consumers who only need core WidgetBase functionality.

This would leave:

1. Stateful, which I think we should consider removing in favour of promoting use of typed class properties for any required internal state.
2. Projector, which would remain as an optional mixin to decorate a widget with functionality required to attach to the DOM.

[kitsonk]

I would be 👍 for Themeable and Registry. I guess how heavy is I18n overall? It feels sort of 50/50 it being fundamental. Are all @dojo/widgets using it?

I think with Stateful we don't have a compelling use case at the moment, between meta and potentially injectors with whatever "app" becomes. Agree with Projector comments.

[kitsonk]

@agubler is this still valid (undone)? I don't think it is a discussion anymore because we all think it is a 👍. If still to do, will it make beta4, or should we move it to beta5?

[agubler]

@kitsonk perhaps with the changes coming to Themeable meaning it's only needed when theming is required, not to just use classes full stop, we could possibly leave it separate.

[kitsonk]

@agubler any further action on this? It feels that with other changes we have largely mitigated this issue?

[agubler]

Completely mitigated in my opinion, closing.