feat: new @typespec/rest-api library with standard REST terminology

[Copilot]

New TypeSpec library for defining RESTful APIs using widely understood REST terminology. Not based on the existing @typespec/rest package — clean-slate design with breaking changes allowed.

Decorators

• @resource(collectionName) / @parentResource(parent) — define resources and nested hierarchies
• @reads, @creates, @updates, @deletes, @lists, @createsOrReplaces — map operations to HTTP verbs
• @action(name?) / @collectionAction(resourceType, name?) — custom endpoints beyond CRUD

CRUD template interfaces

Composable interfaces: ReadOperations, CreateOperations, UpdateOperations, DeleteOperations, ListOperations, CreateOrReplaceOperations, plus aggregates InstanceOperations, CollectionOperations, and CrudOperations.

Helper models

KeysOf<T>, ParentKeysOf<T>, ResourceKey<T>, CollectionKey<T> for key parameter composition.

Example

import "@typespec/rest-api";
using TypeSpec.RestApi;

@resource("pets")
model Pet {
  @key("petId") id: string;
  name: string;
}

@resource("toys")
@parentResource(Pet)
model Toy {
  @key("toyId") id: string;
  name: string;
}

@error model ApiError { code: int32; message: string; }

interface Pets extends CrudOperations<Pet, ApiError> {}
interface PetToys extends ReadOperations<Toy, ApiError>, ListOperations<Toy, ApiError> {}

19 unit tests covering all decorators, diagnostic validation, and template interfaces.

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