Feature: #106640 - Localize enum labels in site settings definitions

Description

Enum option labels in site settings definitions can now be localized consistently.

This applies to all common enum declaration styles:

List-style enum declarations derive localization keys using settings.<settingKey>.enum.<enumValue> in the set labels file.
Map-style enum declarations are independent of that key schema: only the configured label value is evaluated.
Map-style enum declarations with localization references (LLL:...) resolve these references.
Map-style enum declarations with literal labels keep these labels as-is.
Map-style key-only enum entries fall back to the enum value.
Map-style empty string labels remain empty strings.

Example

List-style enum declaration in settings.definitions.yaml

settings:
  my.enumSetting:
    type: string
    default: optionA
    enum:
      - optionA
      - optionB

Matching labels in labels.xlf

<trans-unit id="settings.my.enumSetting.enum.optionA">
  <source>Option A (localized)</source>
</trans-unit>
<trans-unit id="settings.my.enumSetting.enum.optionB">
  <source>Option B (localized)</source>
</trans-unit>

Map-style enum declaration in settings.definitions.yaml

settings:
  my.enumSetting:
    type: string
    default: optionA
    enum:
      optionA: 'LLL:EXT:my_extension/Configuration/Sets/MySet/labels.xlf:settings.custom.optionA' # Explicit LLL reference
      optionB: 'Literal Option B' # Literal label
      optionC: # Key-only map-style entry, falls back to enum value "optionC"
      optionD: '' # Empty label stays empty

Referenced label in labels.xlf

<trans-unit id="settings.custom.optionA">
  <source>Option A (localized)</source>
</trans-unit>

If you want to work with automatically derived keys in the set labels.xlf (for example settings.<settingKey>.enum.<enumValue>), omit enum labels in YAML and use list-style enum declarations.

Impact

Integrators can localize enum options consistently using the same resolution behavior as other setting labels.