Update component tests to always use the YAML examples

[vanitabarrett]

Part of: #1830

What

• Update component tests to consistently use the examples in the YAML files.
• Update component tests and YAML examples to add any missing tests.
• Add a flag to hide examples that we don't want shown in the GOVUK Frontend review app.
• Add a html param and example to the fieldset component. It uses caller, but should have an alternative.

Why

We will be generating fixtures from these YAML examples. We want to make sure the YAML files properly represent what data can be passed to each component and that these are tested.