Add rename-types transformer to graphql package

[FionaBronwen]

Summary

This PR adds the rename-types transform to the @typespec/graphql package, which sanitizes TypeSpec type names into valid GraphQL identifiers using the new compiler transformer infrastructure.

What It Does

The rename-types transform applies sanitizeNameForGraphQL() to:

• Models - $My-Model$ → _My_Model_
• Model properties - my.prop → my_prop
• Enums - My.Enum → My_Enum
• Enum members - 123value → _123value
• Operations - my-query → my_query
• Scalars - $CustomScalar$ → _CustomScalar_

The sanitization replaces non-word characters with underscores and prefixes names starting with numbers.

Usage

# tspconfig.yaml
transformer:
  extends: ["@typespec/graphql/graphql_naming"]

Or enable individually:

transformer:
  enable:
    "@typespec/graphql/rename-types": true

Changes

File	Description
src/transformers/rename-types.transform.ts	Transform definition with mutation classes for each type kind
src/transformer.ts	Exports $transformer with the graphql_naming transform set
src/lib/type-utils.ts	sanitizeNameForGraphQL() utility (existing file, function already present)
test/transformers/rename-types.transform.test.ts	Comprehensive tests for all type kinds
package.json	Added @typespec/mutator-framework dependency

Testing

pnpm -F @typespec/graphql exec vitest run test/transformers/rename-types.transform.test.ts