Document new translation (i18n) support

[sdirix]

MVP:

• Add a new page to the docs called i18n
• Explain the concept i18n: (locale, translate, translateError) given via props
• Add the new props to the bindings documentation
• Mention that the renderer sets themselves are not yet translated, link to issue in JSON Forms: Translate hard coded strings in existing renderer sets jsonforms#1826
• i18n key in UI Schema options, i18n key in JSON Schema, otherwise default generated based on the property path.
• Default Error Translation:
  • <i18nkey>.error.custom: Single message no matter how many errors are there
  • <i18nkey>.error.<keyword> e.g. name.error.required or name.error.pattern,
  • error.<keyword>, e.g. error.required, error.pattern
  • should match pattern [0-9]+
• Enum Translations
• Translate function should be side effect free and should be stable (memoized) to avoid unnecessary rerenderings, i.e. the translate function should only change if there are new translations.
• Showcase how to access locale, translate and translateError in custom renderers (React). const ctx = useJsonForms(). Mention that for example locale can be used for number formatting.

Polished:

• Showcase translation examples

  • default keys
  • i18n keys
  • default messages

• Showcase integration with react-intl

• There is a live demo of translation support in Vue-Vanilla dev setup