Fix Typedarray.slice fastpath when the content type is matching

[rerobika]

This patch fixes #4888.

JerryScript-DCO-1.0-Signed-off-by: Robert Fancsik robert.fancsik@h-lab.eu

[dbatyai]

What if count is less than the target offset? I don't think this condition is correct.

var buf = new ArrayBuffer(10);
var a1 = new Int8Array(buf, 0, 5);
a1.fill(1);
a1.constructor = {
    [Symbol.species]: function (len) {
        return new Int8Array(buf, 5, 5);
    }
};
var a2 = a1.slice(2,4);
res = new Int8Array(buf, 0, 10);

Also, I don't think checking the offset is the right way, we need to check whether the two typedarrays use the same arraybuffer instead, and only then fall back to copying element-by-element.