[test] Make mjsunit harness more robust to fuzzers

Some fuzzers replaced strigify and then caused uncaught errors
from harness methods using prettyPrinted.

Bug: chromium:1102897
Change-Id: I7ae6a90040ba0aa5ec1efa4a8b73e053ec75dd79
Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/2304814
Auto-Submit: Michael Achenbach <machenbach@chromium.org>
Reviewed-by: Maya Lekova <mslekova@chromium.org>
Commit-Queue: Maya Lekova <mslekova@chromium.org>
Cr-Commit-Position: refs/heads/master@{#68947}

test/mjsunit/mjsunit.js

@@ -216,6 +216,7 @@ var prettyPrinted;
   var ArrayPrototypeJoin = Array.prototype.join;
   var ArrayPrototypeMap = Array.prototype.map;
   var ArrayPrototypePush = Array.prototype.push;
+  var JSONStringify = JSON.stringify;
 
   var BigIntPrototypeValueOf;
   // TODO(neis): Remove try-catch once BigInts are enabled by default.
@@ -252,7 +253,7 @@ var prettyPrinted;
   prettyPrinted = function prettyPrinted(value) {
     switch (typeof value) {
       case "string":
-        return JSON.stringify(value);
+        return JSONStringify(value);
       case "bigint":
         return String(value) + "n";
       case "number":