Allow triggerRole to be set

Part of fix for cibernox/ember-power-select-typeahead#67
in `ember-power-select-typeahead`

addon/templates/components/power-select.hbs

@@ -15,6 +15,7 @@
   as |dropdown|}}
 
   {{#dropdown.trigger
+    role=(readonly triggerRole)
     tagName=(readonly _triggerTagName)
     ariaDescribedBy=(readonly ariaDescribedBy)
     ariaInvalid=(readonly ariaInvalid)

tests/dummy/app/templates/public-pages/docs/api-reference.hbs

@@ -280,6 +280,11 @@
       <td><code>string</code></td>
       <td>The id to be applied to the trigger. Useful link the select to a <code>&lt;label&gt;</code> tag</td>
     </tr>
+    <tr>
+      <td>triggerRole</td>
+      <td><code>string</code></td>
+      <td>The aria-role to use on the trigger element. Defaults to <code>'button'</code></td>
+    </tr>
     <tr>
       <td>verticalPosition</td>
       <td><code>string</code></td>

tests/integration/components/power-select/a11y-test.js

@@ -428,3 +428,22 @@ test('Multiple-select: The trigger element correctly passes through WAI-ARIA rel
   assert.equal(trigger.attributes['aria-describedby'].value, 'ariaDescribedByString', 'aria-describedby set correctly');
   assert.equal(trigger.attributes['aria-labelledby'].value, 'ariaLabelledByString', 'aria-required set correctly');
 });
+
+test('Trigger can have a custom aria-role passing triggerRole', function(assert) {
+  assert.expect(2);
+  let role = 'my-role';
+  this.role = role;
+
+  this.numbers = numbers;
+
+  this.render(hbs`
+    {{#power-select options=countries selected=country onchange=(action (mut foo)) triggerRole=role as |country|}}
+      {{country.name}}
+    {{/power-select}}
+  `);
+
+  assert.equal(find('.ember-power-select-trigger').getAttribute('role'), role, 'The `role` was added.');
+
+  this.set('role', undefined);
+  assert.equal(find('.ember-power-select-trigger').getAttribute('role'), 'button', 'The `role` was defaults to `button`.');
+});