extensions/typescript-language-features/src/languageFeatures/callHierarchy.ts/register
export function register(
	selector: DocumentSelector,
	client: ITypeScriptServiceClient
) {
	return conditionalRegistration([
		requireMinVersion(client, TypeScriptCallHierarchySupport.minVersion),
		requireSomeCapability(client, ClientCapability.Semantic),
	], () => {
		return vscode.languages.registerCallHierarchyProvider(selector.semantic,
			new TypeScriptCallHierarchySupport(client));
	});
}