[web] Introduce EditUserAvatarMenu

Summary:
Dropdown menu with edit user avatar options (eg emoji, image, etc).

Depends on D8242

Test Plan:
Looks as expected:

(Used icons + copy from native, the Figma designs are pretty old)

(Right now the menu items appear to the left of the button, will need to modify Menu to be able to display items to the right of the button... will defer this)

Reviewers: ashoat, ginsu

Reviewed By: ashoat

Subscribers: tomek

Differential Revision: https://phab.comm.dev/D8243