[web] Wrap modals with WebEditUserAvatarProvider

Summary:
We want to be able to access eg setUserAvatar from EmojiAvatarSelectionModal, however, we can't access the context since the modal is being rendered outside of "mainContent".

We're only wrapping modals with WebEditUserAvatarProvider when the user is logged in.

Depends on D8268

Test Plan: Able to access EditUserAvatarContext from EmojiAvatarSelectionModal as expected.

Reviewers: ashoat, ginsu, michal, kamil, inka, rohan

Reviewed By: ginsu

Subscribers: tomek

Differential Revision: https://phab.comm.dev/D8269