This CL changes the NumberDictionary fast-path for Array.p.sort to
throw a TypeError when trying to write to a read-only property.

Previously, the fast-path simply bailed to the slow-path which could
swallow the TypeError by accident. I.e. because the fast-path could
leave the array in an inconsistent state that is already sorted.

Example:

let arr = new Array(10);
Object.defineProperty(arr, 0, {value: 2, writable: false});
Object.defineProperty(arr, 2, {value: 1, writable: false});
arr.sort();

The pre-processing step will move the value 1 to index 1: {0: 2, 1: 1}
When trying to swap those 2 values, the fast-path will write the 2 at
index 1, then try to write the 1 at index 0 and fail, bailing to the
slow-path. As the array looks like {0: 2, 1: 2} its already sorted
and the TypeError will not be thrown.

R=jgruber@chromium.org

Bug: v8:7382, v8:7907
Change-Id: I5d2f2d73478fdca066ce1048dcb2b8301751cb1f
Reviewed-on: https://chromium-review.googlesource.com/1122120
Commit-Queue: Simon Zünd <szuend@google.com>
Reviewed-by: Jakob Gruber <jgruber@chromium.org>
Cr-Commit-Position: refs/heads/master@{#54150}