extensions/typescript-language-features/src/languageFeatures/signatureHelp.ts/register
export function register(
	selector: DocumentSelector,
	client: ITypeScriptServiceClient,
) {
	return conditionalRegistration([
		requireSomeCapability(client, ClientCapability.EnhancedSyntax, ClientCapability.Semantic),
	], () => {
		return vscode.languages.registerSignatureHelpProvider(selector.syntax,
			new TypeScriptSignatureHelpProvider(client), {
			triggerCharacters: TypeScriptSignatureHelpProvider.triggerCharacters,
			retriggerCharacters: TypeScriptSignatureHelpProvider.retriggerCharacters
		});
	});
}