[Tests] Add mjsunit test for issue 1076569.

BUG=chromium:1076569

Change-Id: I178e12e20f48dc4216c3f108352425e0aa91047f
Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/2185130
Auto-Submit: Ross McIlroy <rmcilroy@chromium.org>
Commit-Queue: Michael Achenbach <machenbach@chromium.org>
Reviewed-by: Michael Achenbach <machenbach@chromium.org>
Cr-Commit-Position: refs/heads/master@{#67628}

test/mjsunit/regress/regress-1076569.js

+// Copyright 2020 the V8 project authors. All rights reserved.
+// Use of this source code is governed by a BSD-style license that can be
+// found in the LICENSE file.
+// Flags: --allow-natives-syntax --turboprop
+
+var array = new Int16Array();
+
+function foo() {
+  array[0] = "123.12";
+}
+
+%PrepareFunctionForOptimization(foo);
+foo();
+foo();
+%OptimizeFunctionOnNextCall(foo);
+foo();