Fieldset accessibility tests

These tests are intended to test the accessibility of the fieldset and legend elements.

To run these tests, open the browser's developer tools and navigate to the Accessibility pane (may need to activate it in Settings), or use an OS-level accessibility inspector, and verify that the accessible name/role matches the expected accessible name/role.

The following issue discusses ways to automate these tests:

https://github.com/web-platform-tests/wpt/issues/12791