This configured allowed types for config fields so we can check them in future

See: #4230

This prevents circular dependency issues

Since we only pass in `DOMStringMap` values, this removes all tests for `normaliseDataset()` that don’t pass in strings

We also prevent unnecessary data attributes (e.g. `data-module="govuk-accordion"’) from being merged into the config

See: #4230

We can reduce the code we use by expanding dot-separated data-attributes at the point we read them

This lets us remove `flattenConfigs()` since we can use nested configs everywhere

Do you want a `data-example="2024"` to stay as a string?

Data attributes now understand component config schema types

Extra checks added to guard against objects, arrays and non-finite numbers (NaN, Infinity)

…allow keys are set