DEV: Introduce API for rendering Glimmer inside posts (#20140)

`helper.renderGlimmer` will return an HTML element which can be added to a post's `cooked`

Example usage:
```
import { hbs } from "ember-cli-htmlbars";

api.decorateCookedElement((cooked, helper) => {
  const glimmerElement = helper.renderGlimmer(
    "div.my-wrapper-class",
    hbs`<DButton @icon={{@data.param}} @translatedLabel="Hello world from Glimmer Component"/>`,
    { param: "user-plus" }
  );
  cooked.appendChild(glimmerElement);
}, { onlyStream: true, id: "my-id" });
```

See `widgets/render-glimmer.js` for more detailed usage information.

app/assets/javascripts/discourse/tests/acceptance/topic-post-decorate-cooked-test.js

@@ -0,0 +1,51 @@
+import Component from "@glimmer/component";
+import { hbs } from "ember-cli-htmlbars";
+import { setComponentTemplate } from "@ember/component";
+import { test } from "qunit";
+import { acceptance } from "discourse/tests/helpers/qunit-helpers";
+import { visit } from "@ember/test-helpers";
+import { withPluginApi } from "discourse/lib/plugin-api";
+
+acceptance("Acceptance | decorateCookedElement", function () {
+  test("decorator with renderGlimmer works", async function (assert) {
+    class DemoComponent extends Component {
+      static eventLog = [];
+      constructor() {
+        DemoComponent.eventLog.push("created");
+        return super(...arguments);
+      }
+      willDestroy() {
+        DemoComponent.eventLog.push("willDestroy");
+      }
+    }
+    setComponentTemplate(
+      hbs`<span class='glimmer-component-content'>Hello world</span>`,
+      DemoComponent
+    );
+
+    withPluginApi(0, (api) => {
+      api.decorateCookedElement((cooked, helper) => {
+        if (helper.getModel().post_number !== 1) {
+          return;
+        }
+        cooked.appendChild(
+          helper.renderGlimmer(
+            "div.glimmer-wrapper",
+            hbs`<@data.component />`,
+            { component: DemoComponent }
+          )
+        );
+      });
+    });
+
+    await visit("/t/internationalization-localization/280");
+
+    assert.dom("div.glimmer-wrapper").exists();
+    assert.dom("span.glimmer-component-content").exists();
+    assert.deepEqual(DemoComponent.eventLog, ["created"]);
+
+    await visit("/");
+
+    assert.deepEqual(DemoComponent.eventLog, ["created", "willDestroy"]);
+  });
+});