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

spec/javascripts/vue_shared/components/user_avatar_image_spec.js

@@ -47,7 +47,14 @@ fdescribe('User Avatar Image Component', function () {
     });
     it('should properly render img css', function () {
-      expect(this.userAvatarImage.$el.classList.value).toContain('avatar s99 myextraavatarclass');
+      const classList = this.userAvatarImage.$el.classList;
+      const containsAvatar = classList.contains('avatar');
+      const containsSizeClass = classList.contains('s99');
+      const containsCustomClass = classList.contains('myextraavatarclass');
+
+      expect(containsAvatar).toBe(true);
+      expect(containsSizeClass).toBe(true);
+      expect(containsCustomClass).toBe(true);
     });
   });
 });