Add \Drupal\Core\Config\TypedConfigManager::hasTranslatableValues()

Problem/Motivation

At the moment config object require a langcode key when the config is has a translatable value and this is dynamically determined by Locale using schema:

config_object:
  type: mapping
  mapping:
    _core:
      # This only exists for merging configuration; it's not required.
      requiredKey: false
      type: _core_config_info
    langcode:
      requiredKey: false
      type: langcode
  constraints:
    # The `langcode` key:
    # - MUST be specified when there are translatable values
    # - MUST NOT be specified when there are no translatable values.
    # Translatable values are specified for this config schema type (a subtype of `type: config_object`) if the
    # `translatable` flag is present and set to `true` for *any* element in that config schema type.
    LangcodeRequiredIfTranslatableValues: ~

and \Drupal\locale\LocaleConfigManager::getTranslatableData()

This is unreliable as config entities may have third party settings or plugins that add translatable keys and we'll only know that they are translatable if there is a value. This situation is also possible with simple config which has a translatable value that is not required.

This issue blocks #3337864: Introduce a dedicated "Configuration default language" different from "Site default language"

Steps to reproduce

Proposed resolution

• Add \Drupal\Core\Config\TypedConfigManager::hasTranslatableValues() which will return:
• TRUE for all config entities - these always support third party settings so we just do know.
• Will return TRUE if the simple config has updated it's schema to require the langcode
• Will use the complete schema and not values if the schema has requiredKey: false
• The LangcodeRequiredIfTranslatableValues will use the same logic.

Remaining tasks

User interface changes

Introduced terminology

API changes

Data model changes

Release notes snippet