Adds the fileURLToPathBuffer export to node:url.

Like fileURLToPath, but returns the path as a Buffer of raw bytes obtained by percent-decoding the URL without interpreting the result as UTF-8. This allows recovering file paths that contain non-Unicode byte sequences (e.g. Shift-JIS file names) that fileURLToPath cannot decode.

Implements the WHATWG percent-decode algorithm operating on raw bytes, plus posix/win32 path extraction mirroring Node's getPathBufferFromURLPosix / getPathBufferFromURLWin32.

Enables parallel/test-fileurltopathbuffer.js in the node_compat suite, which round-trips a non-Unicode path:

const testPath = new URL('%82%A0%82%A2%82%A4', tmpdirUrl);
// fileURLToPath throws URIError on the non-UTF-8 sequence; the buffer variant succeeds.
assert.ok(existsSync(fileURLToPathBuffer(testPath)));

The target test passes locally (the upstream test skips on macOS and Windows). Adjacent node:url / fileurl tests are unaffected.