String identifiers can't be used with method shorthand

[nzakas]

The following should be legal but throws an error when objectLiteralShorthandMethods is enabled:

var x = {
    "foo"() {
        return bar;
    }
};

[nzakas]

Working on this.

[nzakas]

In the course of working on this issue, I found several addition problems:

First, this is legal but is throwing an error:

var x = {
    get(){}
};

var x = {
    set(){}
};

Also, this is parsing fine but should throw an error:

var x = {
    method() 43
};

[nzakas]

I'm adding a lot more tests for properties as part of this.