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/diff_notes/components/diff_note_avatars.js

@@ -26,7 +26,7 @@ const DiffNoteAvatars = Vue.extend({
         <!-- FIXME: Pass an alt attribute here for accessibility -->
         <user-avatar-image
           class="diff-comment-avatar js-diff-comment-avatar"
-          @click="clickedAvatar($event)"
+          @click.native="clickedAvatar($event)"
           :src="note.authorAvatar"
           :size="19"
           :tooltip-text="getTooltipText(note)"