Bug 1821959 - Add test case. r=jandem

Differential Revision: https://phabricator.services.mozilla.com/D173555

js/src/jit-test/tests/basic/bug1821959.js

@@ -0,0 +1,7 @@
+// Transplant an object that is using the shifted-dense-elements optimization
+const v1 = this.transplantableObject();
+const v2 = v1.object;
+Array.prototype.push.call(v2, 0);
+Array.prototype.push.call(v2, 0);
+Array.prototype.shift.call(v2);
+v1.transplant(newGlobal());