Emit for as operator drops nested module prefix

[NoelAbrahams]

Hi,

Version: TS 1.6

module foo.bar {
    export function baz(){}
};

module foo {
  const a1 = bar['baz']; // foo.bar['baz']
  const a2 = (<any>bar)['baz']; // foo.bar['baz']
  const a3 = (bar as any)['baz'];  // bar['baz']
}

The emit for a3 appears to be wrong.

[mhegazy]

looks like a duplicate of #4832. This should be fixed in typescript@next.