docs: add .gitignore to stackblitz template (#33847)

Adds a `.gitignore` file to the Stackblitz template to prevent `dist` files from showing up for users.

Fixes #33836.

Author: crisbeto

docs/src/app/shared/example-viewer/example-viewer.html

@@ -40,7 +40,7 @@
     </div>
   } @else {
     <div class="docs-example-viewer-title">
-      <p>{{exampleData?.title}}</p>
+      {{exampleData?.title}}
 
       <div class="docs-example-viewer-actions">
         <button

docs/src/app/shared/stackblitz/stackblitz-writer.ts

@@ -45,6 +45,9 @@ export const TEMPLATE_FILES = [
   'tsconfig.app.json',
   'tsconfig.json',
   'tsconfig.spec.json',
+  // We need a gitignore, because harness tests generate files in `dist`
+  // which can prevent users from forking the example (see 33836).
+  '.gitignore',
   'src/index.html',
   'src/main.ts',
   'src/styles.css',

docs/src/assets/stackblitz/.gitignore

@@ -0,0 +1 @@
+dist