fs: makes existsSync stop using errors

[arcanis]

The previous implementation of existsSync was a try/catch on top
of accessSync. While conceptually sound it was a performance problem
when running it repeatedly on non-existing files, because accessSync
had to create an Error object that was immediatly discarded (because
existsSync never reports anything else than true / false).

This implementation simply checks whether the context would have caused
an exception to be thrown, but doesn't actually create it.

I benchmarked it as such:

const fs = require('fs');

console.time();
for (let t = 0; t < 100000; ++t) fs.existsSync('./doesnt-exist');
console.timeEnd();

❯ [mael-mbp?] node git:(existssync-no-errors) ✗ ❯ node --version
v11.1.0

❯ [mael-mbp?] node git:(existssync-no-errors) ✗ ❯ node test.js
default: 2543.314ms

❯ [mael-mbp?] node git:(existssync-no-errors) ✗ ❯ ./node test.js
default: 287.442ms

Fixes: #24008

Checklist

• make -j4 test (UNIX), or vcbuild test (Windows) passes
• tests and/or benchmarks are included
• commit message follows commit guidelines

[mscdex]

I believe this change is already being made in #24015?

[arcanis]

Oh, my bad! I see Github still doesn't send notifs when a PR is attached to an issue .. 😅

[refack]

Oh, my bad!

I wouldn't worry about that. Hope to see you contribute more in the future.