Support overload resolution with type union arguments

TypeScript Version: 2.1.6

Code

interface Foo {
    bar(s: string): void;
    bar(n: number): number;
    bar(b: boolean): boolean;
}
type SN = string | number;

var sn1: string | number;
var sn2: SN;
var foo: Foo;

var x1 = foo.bar(sn1); // error
var x2 = foo.bar(sn2); // error

Expected behavior:
This should be allowed.
The type of x1 and x2 should be void | number, the union of the matching overload return types.

All 3 overloads can be seen as a single overload with a union type. It should try to fallback to a union when it can't match one of the originally defined overloads.

Actual behavior:
error TS2345: Argument of type 'string | number' is not assignable to parameter of type 'boolean'.
Type 'string' is not assignable to type 'boolean'.

Start with the TypeScript reproduction in the issue and inspect how overload resolution handles union arguments and return types. Done means calls with string | number arguments are accepted and infer void | number, while the existing boolean overload behavior remains correct.