Issue 959: Enable auto-completion of built-in members

Steps to reproduce

  1. Verify the following completions:
    • Object.prototype. -> toString (with popup)
    • Object. -> prototype (with popup)
    • Object.getOwn -> PropertyNames (with popup)
    • do -> cument (without popup)
    • document._ -> _proto__ (without popup)
    • obj1. -> aa1 (with popup)
    • obj2. -> aa1 (with popup)
    • obj3. -> (no completion)
    • obj3.t -> oString (without popup)
  2. Verify that the following completions are avoided unless they are the only option (e.g. by creating a similar property in the console)
    • String.prototype.fontco
    • ''.fontco
    • propertyisenumerable
    • alert.arguments
    • document.body.__lookupGetter__
    • document.body.vLink

Expected Results