Cannot use generic types in JsDoc

[billti]

Generic types may not be specified for variable, param, or return types currently. For example, both of the below just show up as 'any's.

/** @type {PromiseLike<string>} */
var a9;

/**
 * @return {PromiseLike<string>}
 */
function f9(){}

We should support this using a syntax like that show above, which closely matches TypeScript's and is covered in the Closure Compiler docs also (https://developers.google.com/closure/compiler/docs/js-for-compiler#instantiating-a-generic-type)