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

@@ -57,7 +57,7 @@ export default {
     <img
       :class="imgCssClasses"
       :src="imgSourceWithFallback"
-      :style="sizeStylesMap"
+      :style="avatarSizeStylesMap"
       :alt="alt"
       :data-container="tooltipContainer"
       :data-placement="tooltipPlacement"