Add arm-no-replace-inherited-props linting rule

[Copilot]

Redefining a property already declared on a base model is an Azure API anti-pattern and currently crashes the breaking-change tool (see azure-rest-api-specs#42903). This PR adds a new ARM linter rule to flag the pattern at design time.

Changes

• New rule arm-no-replace-inherited-props (packages/typespec-azure-resource-manager/src/rules/arm-no-replace-inherited-props.ts)
  • Walks baseModel chain; emits a warning for any property in the current model whose name also appears in any ancestor.
  • Exemptions: the name property of an ARM resource, and any property whose name matches a discriminator declared via @discriminator on an ancestor.
  • Diagnostic message: The property '${propertyName}' is also defined in the base model. Redefining inherited properties can cause problems with OpenAPI tooling and some language representations of the models.
• Registration in src/linter.ts (included in the all ruleset).
• Tests covering: clean inheritance, direct override, transitive ancestor override, ARM name exemption, discriminator exemption, and that non-discriminator properties under a @discriminator base are still reported.
• Docs: new rule page plus regenerated linter.md reference and package README.md.
• Changeset under .chronus/changes/.

Example

@armProviderNamespace
namespace MyService;

@discriminator("kind")
model Pet {
  kind: string;
  weight: int32;
}

model Cat extends Pet {
  kind: "cat";    // OK — discriminator
  weight: int32;  // ⚠ arm-no-replace-inherited-props
}