UI: simplify chat thread title (#29998)

We were using a complex logic to make it change size based on scroll position but this was imperfect and not visually pleasing. Also the title had been made a button which was causing the ellipsis to not work correctly, and I would prefer to not mix page knowledge (thread) with title component so I made this click logic directly in the chat-thread component.

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Co-authored-by: Jordan Vidrine <jordan@jordanvidrine.com>

plugins/chat/test/javascripts/components/chat-thread-heading-test.gjs

@@ -0,0 +1,30 @@
+import { getOwner } from "@ember/owner";
+import { render } from "@ember/test-helpers";
+import { module, test } from "qunit";
+import { setupRenderingTest } from "discourse/tests/helpers/component-test";
+import ChatThreadHeading from "discourse/plugins/chat/discourse/components/chat-thread-heading";
+import ChatFabricators from "discourse/plugins/chat/discourse/lib/fabricators";
+
+module("Discourse Chat | Component | chat-thread-heading", function (hooks) {
+  setupRenderingTest(hooks);
+
+  test("it renders the title", async function (assert) {
+    const thread = new ChatFabricators(getOwner(this)).thread({
+      title: "A nice thread title",
+    });
+
+    await render(<template><ChatThreadHeading @thread={{thread}} /></template>);
+
+    assert.dom(".chat-thread__heading-title").hasText("A nice thread title");
+  });
+
+  test("it doesn’t render heading when no title", async function (assert) {
+    const thread = new ChatFabricators(getOwner(this)).thread({
+      title: null,
+    });
+
+    await render(<template><ChatThreadHeading @thread={{thread}} /></template>);
+
+    assert.dom(".chat-thread__heading").doesNotExist();
+  });
+});