Change ParamaterDecorator to allow an undefined propertyKey (microsoft#53365)

Author: dhritzkiv

src/lib/decorators.legacy.d.ts

@@ -1,4 +1,4 @@
 declare type ClassDecorator = <TFunction extends Function>(target: TFunction) => TFunction | void;
 declare type PropertyDecorator = (target: Object, propertyKey: string | symbol) => void;
 declare type MethodDecorator = <T>(target: Object, propertyKey: string | symbol, descriptor: TypedPropertyDescriptor<T>) => TypedPropertyDescriptor<T> | void;
-declare type ParameterDecorator = (target: Object, propertyKey: string | symbol, parameterIndex: number) => void;
+declare type ParameterDecorator = (target: Object, propertyKey: string | symbol | undefined, parameterIndex: number) => void;