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_svg.js

@@ -15,7 +15,6 @@ export default {
   },
   template: `
     <svg
-      v-if="svg"
       :class="avatarSizeClass"
       :styles="avatarSizeStylesMapString"
       v-html="svg"