fs: improve fsPromises writeFile performance

Increase the write chunk size in fsPromises writeFile
to improve performance.

Author: Linkgoron

lib/internal/fs/promises.js

@@ -7,7 +7,7 @@ const kIoMaxLength = 2 ** 31 - 1;
 // Note: This is different from kReadFileBufferLength used for non-promisified
 // fs.readFile.
 const kReadFileMaxChunkSize = 2 ** 14;
-const kWriteFileMaxChunkSize = 2 ** 14;
+const kWriteFileMaxChunkSize = 512 ** 1024;
 
 const {
   ArrayPrototypePush,