Add GraphQL name sanitization utilities

[FionaBronwen]

Summary

Adds utility functions for transforming TypeSpec names into valid GraphQL identifiers. These utilities form the foundation for name handling throughout the GraphQL emitter.

Changes

• src/lib/type-utils.ts - Core utility functions for GraphQL name transformations
• test/lib/type-utils.test.ts - Unit tests for sanitizeNameForGraphQL

Utilities Added

Function	Purpose
sanitizeNameForGraphQL	Sanitize names to be valid GraphQL identifiers
toTypeName	Convert to PascalCase for type names
toFieldName	Convert to camelCase for field names
toEnumMemberName	Convert to CONSTANT_CASE for enum members
getUnionName	Generate names for anonymous unions
getTemplatedModelName	Generate names for templated models (e.g., ListOfString)
isArray, isRecordType	Type guards for array/record models
unwrapModel, unwrapType	Extract element types from arrays
isTrueModel	Check if a model should emit as GraphQL object type
getGraphQLDoc	Extract doc comments for GraphQL descriptions

[steverice]

We should leave this out; this was for internal debugging only.
In https://github.com/pinternal/pinboard/commit/2b03704068544b570ab1cb5cb065ecfc74c05134 it was changed to be behind an emitter config option, which I don't think we need to support here.

[steverice]

nit:

Suggested change

	const args = type.templateMapper.args.filter(isNamedType).map((arg) => getTypeName(arg));
	const args = type.templateMapper.args.filter(isNamedType).map(getTypeName);

[steverice]

All of the prefixing logic (here and elsewhere) should be removed from these utils. In a mutator world, it makes a lot more sense as a separate (and very straightforward) mutation.

[steverice]

Suggested change

	/**
	* Check if a model is an array type.
	*/
	export function isArray(model: Model): model is ArrayModelType {
	return Boolean(model.indexer && model.indexer.key.name === "integer");
	}
	/**
	* Check if a model is a record/map type.
	*/
	export function isRecordType(type: Model): type is RecordModelType {
	return Boolean(type.indexer && type.indexer.key.name === "string");
	}

As noted here, these should be removed in favor of using the equivalent functions in typespec/compiler. Those take a program argument but don't actually use it, so perhaps we can open a PR to deprecate the argument and make it optional.