JSDoc Allow {} around typecasts/declarations to be optional

[weswigham]

TypeScript Version: 2.7.0-dev.201xxxxx

Code

        this._cachedTypeClasses[typeName] = /** @type function(new:Object) */ (object);

Expected behavior:
object cast to function(new:Object)

Actual behavior:

front_end/Runtime.js(398,24): error TS1138: Parameter declaration expected.

(Parse error on function keyword)

We've seen this before (and crashed on it), but choose not to make it not an error because it seemed wrong; however a lot of code that validates under closure compiler (namely the chrome devtools) appears to be written like this.