FEATURE: Support for publishing topics as pages (#9364)

If the feature is enabled, staff members can construct a URL and publish a
topic for others to browse without the regular Discourse chrome.

This is useful if you want to use Discourse like a CMS and publish
topics as articles, which can then be embedded into other systems.

test/javascripts/acceptance/page-publishing-test.js

@@ -0,0 +1,40 @@
+import { acceptance } from "helpers/qunit-helpers";
+
+acceptance("Page Publishing", {
+  loggedIn: true,
+  pretend(server, helper) {
+    const validSlug = helper.response({ valid_slug: true });
+
+    server.put("/pub/by-topic/280", () => {
+      return helper.response({});
+    });
+    server.get("/pub/by-topic/280", () => {
+      return helper.response({});
+    });
+    server.get("/pub/check-slug", req => {
+      if (req.queryParams.slug === "internationalization-localization") {
+        return validSlug;
+      }
+      return helper.response({
+        valid_slug: false,
+        reason: "i don't need a reason"
+      });
+    });
+  }
+});
+QUnit.test("can publish a page via modal", async assert => {
+  await visit("/t/internationalization-localization/280");
+  await click(".topic-post:eq(0) button.show-more-actions");
+  await click(".topic-post:eq(0) button.show-post-admin-menu");
+  await click(".topic-post:eq(0) .publish-page");
+
+  await fillIn(".publish-slug", "bad-slug");
+  assert.ok(!exists(".valid-slug"));
+  assert.ok(exists(".invalid-slug"));
+  await fillIn(".publish-slug", "internationalization-localization");
+  assert.ok(exists(".valid-slug"));
+  assert.ok(!exists(".invalid-slug"));
+
+  await click(".publish-page");
+  assert.ok(exists(".current-url"));
+});