fix(isArrayLike): correctly handle string primitives

[mernen]

Fix for #3713:

The isArrayLike test in 1.0 worked properly with any string values, returning true (since they can be indexed just like String objects and work with functions like Array.prototype.forEach). The new test in 1.2 (introduced by #3356) raises a TypeError, because the in operator cannot be used on a non-object.

Since there are no tests for the private isArrayLike, I'm including a test for angular.forEach, its main caller.

[dcherman]

FYI, functions have a .length property which is why the jQuery implementation was explicitly making sure it wasn't a function. Should probably continue to handle that case so functions aren't treated as ArrayLike

[mernen]

That's now handled by the typeof test above, as callables have their own type even though they are technically objects.

[btford]

isArrayLike should return false for strings.

We discussed this, and here (for the history books) is what @IgorMinar said:

hear ye, hear ye from this point onward, strings shall not be considered array-like -- Igor Minar on Oct 2, in the year 2013

The reason for this is that this helper is used primarily to determine the behavior for ngRepeat, and prevents weird behavior when trying to iterate over characters in a string.

If you do want to iterate over the characters of a string like this, you can simply explode the string into an array of characters with str.split('').

We changed our minds. Strings shall be array-like. Programming is hard.

[btford]

Landed as 5b8c788. Thanks!