util: use let instead of var for util/inspect.js

PR-URL: #30399
Reviewed-By: James M Snell <jasnell@gmail.com>
Reviewed-By: Colin Ihrig <cjihrig@gmail.com>
Reviewed-By: Gireesh Punathil <gpunathi@in.ibm.com>
Reviewed-By: Ruben Bridgewater <ruben@bridgewater.de>
Reviewed-By: Trivikram Kamat <trivikr.dev@gmail.com>

lib/internal/util/inspect.js

@@ -1133,7 +1133,7 @@ function formatPrimitive(fn, value, ctx) {
 
 function formatNamespaceObject(ctx, value, recurseTimes, keys) {
   const output = new Array(keys.length);
-  for (var i = 0; i < keys.length; i++) {
+  for (let i = 0; i < keys.length; i++) {
     try {
       output[i] = formatProperty(ctx, value, recurseTimes, keys[i],
                                  kObjectType);
@@ -1221,7 +1221,7 @@ function formatArray(ctx, value, recurseTimes) {
 
   const remaining = valLen - len;
   const output = [];
-  for (var i = 0; i < len; i++) {
+  for (let i = 0; i < len; i++) {
     // Special handle sparse arrays.
     if (!hasOwnProperty(value, i)) {
       return formatSpecialArray(ctx, value, recurseTimes, len, output, i);
@@ -1297,7 +1297,7 @@ function formatSetIterInner(ctx, recurseTimes, entries, state) {
   const maxLength = Math.min(maxArrayLength, entries.length);
   let output = new Array(maxLength);
   ctx.indentationLvl += 2;
-  for (var i = 0; i < maxLength; i++) {
+  for (let i = 0; i < maxLength; i++) {
     output[i] = formatValue(ctx, entries[i], recurseTimes);
   }
   ctx.indentationLvl -= 2;
@@ -1465,7 +1465,7 @@ function isBelowBreakLength(ctx, output, start, base) {
   let totalLength = output.length + start;
   if (totalLength + output.length > ctx.breakLength)
     return false;
-  for (var i = 0; i < output.length; i++) {
+  for (let i = 0; i < output.length; i++) {
     if (ctx.colors) {
       totalLength += removeColors(output[i]).length;
     } else {
@@ -1579,7 +1579,7 @@ function formatWithOptions(inspectOptions, ...args) {
     let tempStr;
     let lastPos = 0;
 
-    for (var i = 0; i < first.length - 1; i++) {
+    for (let i = 0; i < first.length - 1; i++) {
       if (first.charCodeAt(i) === 37) { // '%'
         const nextChar = first.charCodeAt(++i);
         if (a + 1 !== args.length) {