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.vue

@@ -56,7 +56,7 @@ export default {
   <img
     :class="imgCssClasses"
     :src="imgSrc"
-    :style="avatarSizeStylesMapString"
+    :style="avatarSizeStylesMap"
     :alt="imgAlt"
     :data-container="tooltipContainer"
     :data-placement="tooltipPlacement"