Consolidate user avatar Vue logic

Creates 3 vue components:

1. user-avatar-link
2. user-avatar-image
3. user-avatar-svg

and implements them in several places.

Closes https://gitlab.com/gitlab-org/gitlab-ce/issues/31017

• Port to EE
• Test each implementation manually

EE Compatible Branch: https://gitlab.com/gitlab-org/gitlab-ee/merge_requests/1699

app/assets/javascripts/vue_shared/components/user_avatar/user_avatar_image.js

@@ -2,7 +2,7 @@ import UserAvatarSizeMixin from './user_avatar_size_mixin';
 export default {
   name: 'UserAvatarImage',
-  mixins: [ UserAvatarSizeMixin ],
+  mixins: [UserAvatarSizeMixin],
   props: {
     src: {
       type: String,