perf: optimize Buffer.from("base64") for forgiving-base64 conforming input

[littledivy]

Don't try to clean the input unless decoding fails at first. A ~3x improvement for forgiving-base64 conforming input.

$ target/release/deno run  -A ./bench.mjs
593.3049169
$ deno run -A ./bench.mjs
1912.209888
$ node bench.mjs
989.406209

import { Buffer } from "node:buffer";

const buffer = Buffer.alloc(1024 * 10, "latin1");
const input = buffer.toString("base64");
const start = performance.now();
for (let i = 0; i < 100000; i++) {
	Buffer.from(input, "base64");
}

console.log(performance.now() - start);

Ref #24323

[bartlomieju]

Nice work!