Start expanding the library's public API

Brief

Start expanding the public API of GOV.UK Frontend by opening some features for initialising components:

checking if GOV.UK Frontend is supported in a consistent way
initialising GOV.UK Frontend components and service components the same way
offering a base component class checking GOV.UK Frontend support and storing the root element of components

Ensure these features are documented in the Frontend docs, with both:

guidance on how to use them
an API reference of the classes/functions that provide them (and their properties/methods/arguments/return values...)

This is a first step towards maintaining a wider public API both for using our components and creating components in services.

Epic lead

@romaricpascal

Driving role(s)

@seaemsi, @patrickpatrickpatrick

Supporting roles

Needs awareness

Further detail

### Expanding the API
- [ ] https://github.com/alphagov/govuk-frontend/issues/5209
- [ ] https://github.com/alphagov/govuk-frontend/issues/5210
- [ ] https://github.com/alphagov/govuk-frontend/issues/5213
- [ ] https://github.com/alphagov/govuk-design-system/issues/3812
- [ ] https://github.com/alphagov/govuk-frontend/issues/5211
- [ ] https://github.com/alphagov/govuk-frontend/issues/5212
- [ ] https://github.com/alphagov/govuk-frontend/issues/5214
- [ ] [Stretch] https://github.com/alphagov/govuk-frontend/issues/1127
- [ ] https://github.com/alphagov/govuk-frontend/issues/5267
- [ ] https://github.com/alphagov/govuk-frontend/issues/5216
- [ ] https://github.com/alphagov/govuk-frontend/issues/5217
- [ ] https://github.com/alphagov/govuk-frontend/issues/5225
- [ ] https://github.com/alphagov/govuk-frontend/issues/5215

### Documenting the API
- [ ] https://github.com/alphagov/govuk-frontend/issues/5224
- [ ] https://github.com/alphagov/govuk-frontend-docs/issues/462
- [ ] https://github.com/alphagov/govuk-frontend/issues/5227
- [ ] Add documentation for isSupported to the Frontend docs
- [ ] Add documentation for the updates to `createAll` to the Frontend docs
- [ ] Add documentation for the base component class to the Frontend docs

### Admin
- [x] Initialise decision log (based on Navigation one)
- [x] Document the state we aim for at the end of the cycle

alphagov / govuk-frontend

Start expanding the library's public API #5205