Migrate component data to ES modules

[colinrotherham]

This PR migrates our component data YAML into ES modules to:

1. Run type checks using TypeScript
2. Run code quality checks using ESLint
3. In future, import typed examples into tests without JSON conversion

This is important because we've accidentally missed things in the past:

• Confused by the documentation for radios 'conditional' #1903

But makes it a lot easier to add automated tests for:

• Test that documented component options match the templates #1139

Migration script

See branch component-migrator to convert YAML to ES modules via:

npm exec --workspace packages/govuk-frontend -- gulp fixtures

[colinrotherham]

Would appreciate your non-urgent thoughts on this one @36degrees

Using ES modules found some issues to fix so far:

1. Missing property { required } in Checkboxes nested options for conditional fields
2. Missing property { required } in Radios nested options for conditional fields
3. Missing property { description } in Summary list 'key.html' row parameter
4. Missing JSDoc type for example previewLayoutModifiers from #3808
5. Missing JSDoc type for example description

That's before we've picked up:

• Test that documented component options match the templates #1139

[colinrotherham]

Just rebasing since #2261 and tsc has caught another descrption typo in task-list.yaml

[romaricpascal]

Sounds a neat way to catch errors, and gives us some nice way to catch which component options use specific fields (like isComponent). 😍

No qualms on the naming which sounds fine to me (and nice to separate the params from the examples in different files as well).

Besides fixing the tests, Ollie suggested it could be good to present this to the whole team to take the temperature on not using YAML anymore, as it's a quite different authoring experience (especially for examples) 😊

[querkmachine]

Closing for housekeeping and because there doesn't seem to be much appetite to pursue this at the moment.