assert,util: fix sparse array comparison

Comparing sparse arrays did not work properly. That is fixed and
tests were added to verify that everything works as expected.

This had an impact on `util.isDeepStrictEqual()` and
`assert.deepStrictEqual()` and their counterpart
`assert.notDeepStrictEqual()`.

PR-URL: nodejs#24749
Reviewed-By: Anna Henningsen <anna@addaleax.net>
Reviewed-By: Michaël Zasso <targos@protonmail.com>

lib/internal/util/comparisons.js

@@ -543,11 +543,10 @@ function objEquiv(a, b, strict, keys, memos, iterationType) {
       } else {
         // Array is sparse.
         const keysA = objectKeys(a);
-        i++;
         for (; i < keysA.length; i++) {
           const key = keysA[i];
           if (!hasOwnProperty(b, key) ||
-              !innerDeepEqual(a[key], b[i], strict, memos)) {
+              !innerDeepEqual(a[key], b[key], strict, memos)) {
             return false;
           }
         }

test/parallel/test-assert-deep.js

@@ -557,9 +557,20 @@ assertNotDeepOrStrict(
   assertDeepAndStrictEqual(m3, m4);
 }
 
-// Handle sparse arrays
-assertDeepAndStrictEqual([1, , , 3], [1, , , 3]);
-assertOnlyDeepEqual([1, , , 3], [1, , , 3, , , ]);
+// Handle sparse arrays.
+{
+  assertDeepAndStrictEqual([1, , , 3], [1, , , 3]);
+  assertOnlyDeepEqual([1, , , 3], [1, , , 3, , , ]);
+  const a = new Array(3);
+  const b = new Array(3);
+  a[2] = true;
+  b[1] = true;
+  assertNotDeepOrStrict(a, b);
+  b[2] = true;
+  assertNotDeepOrStrict(a, b);
+  a[0] = true;
+  assertNotDeepOrStrict(a, b);
+}
 
 // Handle different error messages
 {