FEATURE: Don't display muted/ignored users under "who liked" (#10084)

* FEATURE: Don't display muted/ignored users under "who liked"

Previously, if you clicked on the heart icon below a post
it would show you the avatar for a user even if you ignored or muted
them.

This commit will instead display a (?) icon. The count of likes will
remain correct, but you needn't be reminded of the person you
preferred not to see.

* Use a circle instead of (?) for unknown user

test/javascripts/widgets/small-user-list-test.js

@@ -0,0 +1,20 @@
+import { moduleForWidget, widgetTest } from "helpers/widget-test";
+
+moduleForWidget("small-user-list");
+
+widgetTest("renders avatars and support for unknown", {
+  template: '{{mount-widget widget="small-user-list" args=args}}',
+  beforeEach() {
+    this.set("args", {
+      users: [
+        { id: 456, username: "eviltrout" },
+        { id: 457, username: "someone", unknown: true }
+      ]
+    });
+  },
+  async test(assert) {
+    assert.ok(find("[data-user-card=eviltrout]").length === 1);
+    assert.ok(find("[data-user-card=someone]").length === 0);
+    assert.ok(find(".unknown").length, "includes unkown user");
+  }
+});