Add post-form component scaffold

`ember g component post-form`

Rather than just getting the test to pass by putting a form input on the route's template, we "write the code we wish we had." In this case, we wish we had a `post-form` component to use that would provide the form inputs for us. We generate it and go ahead and render it in our route template.

app/components/post-form.js

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+import Component from '@ember/component';
+
+export default Component.extend({
+});

app/templates/components/post-form.hbs

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+{{yield}}

app/templates/posts/new.hbs

@@ -1 +1,3 @@
-{{outlet}}
+<h1>New Post</h1>
+
+<PostForm />

tests/integration/components/post-form-test.js

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+import { module, test } from 'qunit';
+import { setupRenderingTest } from 'ember-qunit';
+import { render } from '@ember/test-helpers';
+import hbs from 'htmlbars-inline-precompile';
+
+module('Integration | Component | post-form', function(hooks) {
+  setupRenderingTest(hooks);
+
+  test('it renders', async function(assert) {
+    // Set any properties with this.set('myProperty', 'value');
+    // Handle any actions with this.set('myAction', function(val) { ... });
+
+    await render(hbs`{{post-form}}`);
+
+    assert.equal(this.element.textContent.trim(), '');
+
+    // Template block usage:
+    await render(hbs`
+      {{#post-form}}
+        template block text
+      {{/post-form}}
+    `);
+
+    assert.equal(this.element.textContent.trim(), 'template block text');
+  });
+});