[tools] Refactor, use built-in Array.flat() instead of custom flatten method

Change-Id: I0e4de2d943db5a6af41bb1a1599e0ebb0568d290
Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/2912881
Reviewed-by: Camillo Bruni <cbruni@chromium.org>
Commit-Queue: Victor Gomes <victorgomes@chromium.org>
Cr-Commit-Position: refs/heads/master@{#74849}

AUTHORS

@@ -228,6 +228,7 @@ Victor Costan <costan@gmail.com>
 Vlad Burlik <vladbph@gmail.com>
 Vladimir Krivosheev <develar@gmail.com>
 Vladimir Shutoff <vovan@shutoff.ru>
+Wael Almattar <waelsy123@gmail.com>
 Wei Wu <lazyparser@gmail.com>
 Wenlu Wang <kingwenlu@gmail.com>
 Wenyu Zhao <wenyu.zhao@anu.edu.au>

tools/tracing/proto-converter/proto-to-json.ts

@@ -24,9 +24,6 @@ import { Root } from 'protobufjs';
 // JSON fields it will include/exclude based on the data present in the trace
 // event.
 
-// TODO(petermarshall): Replace with Array#flat once it lands in Node.js.
-const flatten = <T>(a: T[], b: T[]) => { a.push(...b); return a; }
-
 // Convert a string representing an int or uint (64 bit) to a Number or throw
 // if the value won't fit.
 function parseIntOrThrow(int: string) {
@@ -124,7 +121,7 @@ async function main() {
           }, {})
         };
       }))
-      .reduce(flatten, [])
+      .flat()
   };
   await fs.promises.writeFile(process.argv[4], JSON.stringify(output, null, 2));
 }