refactor(dart): align enum description field name with the DefaultCodegen

[Mattias-Sehlstedt]

This changes how enum descriptions are handled in Dart, and aligns the behavior with the DefaultCodegen.

The behavioral change is that we look for enumDescription rather than description in allowableValues -> enumVars. This can unexpectedly affect a consumer that redefines the template, since now the codegen will expose enumDescription rather than description. The fallback is the update the local template to also use enumDescription.

The change from description to enumDescription also ensures that the enum's own description is not leaked to each enum item. This occurs now when the enum items do not have a description themselves, which in turn makes the mustache parses look further up the tree for a value (and thus find the CodegenModel's description). An enum like the one below is an example that would leak the description.

components:
  schemas:
    Order:
      status:
        type: string
        description: Order Status
        enum:
          - placed
          - approved
          - delivered

I have instead aligned all Dart enum classes so that they place the schema description once on the class itself instead. This behavior already exists on some enums.

The interpretation of the vendor extension x-enum-values have also been extracted to the EnumUtils since it is a format that comes from Bungie, and it might be of interest to use in other Codegens too. See for example #1486.

PR checklist

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Dart commitee:
@jaumard (2018/09) @amondnet (2019/12) @sbu-WBT (2020/12) @kuhnroyal (2020/12) @agilob (2020/12) @ahmednfwela (2021/08)

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Summary by cubic

Aligns Dart enum descriptions with DefaultCodegen: enum items now expose enumDescription, and the schema description is emitted once on the enum type. Standardizes Bungie x-enum-values handling and updates templates, tests, and samples.

• Refactors

  • Update built_value and json_serializable templates (inline and non-inline) to read enumDescription for item docs and render the enum’s description once at the type.
  • Centralize x-enum-values parsing in EnumUtils (BUNGIE_X_ENUM_VALUES, getBungieEnumValues) and use it in AbstractDartCodegen; tests and samples updated to expect enumDescription.

• Migration

  • If you customized Dart enum templates, replace enum item description with enumDescription.

^{Written for commit 38796f6. Summary will update on new commits.}

[cubic-dev-ai]

All reported issues were addressed across 27 files

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