[core] Extend core/i18n substates with actions to set schema and uischema

[edgarmueller]

This PR introduces changes that are meant to be used in the following fashion:

During initialization one is ought to register the respective localized versions of the schema/UI schemas, e.g.:

const localizedSchemas = new Map<string, JsonSchema>();
localizedSchemas.set('de-DE', deSchema);
localizedSchemas.set('en-US', usSchema);
store.dispatch(Actions.setLocalizedSchemas(localizedSchemas));

Likewise for UI schemas.

Then, within the locale switcher of the respective app (which needs to be custom anyway, I think), locales can be switched via the new actions (this could be probably be improved a bit since we need to pass the entire state ATM):

changeLocale(locale: string) {
  store.dispatch(setLocale(locale));
  store.dispatch(setSchema(getLocalizedSchema(locale)(store.getState())));
  store.dispatch(setUISchema(getLocalizedUISchema(locale)(store.getState())));
}

This will cause the root schema/UI schema to be updated and hence the entire forms managed by JSON Forms will be re-rendered with the new schema/UI schema

[coveralls]

Coverage decreased (-0.5%) to 87.504% when pulling bd5dd39 on edgarmueller:feature/core/i18n into 2ba0316 on eclipsesource:master.

[eneufeld]

would it make sense to extend the examples in order to try this feature out?

[edgarmueller]

I'll add the example code I've tested with

[eneufeld]

Awesome