Avatars in sharing dropdown

[PVince81]

Since we have avatars now (as per OC6) we should make them visible here as well:

1. Sharing dropdown in the "shared with" user list
2. In the users autocomplete list from the "Share with" field.

@jancborchardt @karlitschek

I don't think it would fit well in the current dropdown, so we might reconsider it after having revamped it. Linking with the design forward doc: #3224

[Niduroki]

@PVince81 I actually wanted to work on that for OC7 😉 (without redesigning the sharing dropdown though)

[DeepDiver1975]

oc7 will be the "heal sharing release" - let's discuss stuff like this once we are there. THX

[jancborchardt]

The avatars would be helpful with the current dropdown already. @Kondou-ger are you interested in bringing the avatars to sharing?

[Niduroki]

I'll dive into it when I have the time.

[PVince81]

This was added through #13866