Fix bug to make --clear-output-folder work (solution 2)

[msyyc]

• To fix: [Bug] --clear-output-folder does not work for autorest.python > 5.19.0 #1409
• Root cause:
  write_file can't make sure to flush the buffer to disk before black read and format all files from disk:
  

  autorest.python/packages/autorest.python/autorest/jsonrpc/stdstream.py

  Lines 46 to 52 in ba0cb0e

  	def write_message(message: str, stream: BinaryIO = sys.stdout.buffer) -> None:
  	bytes_message = message.encode("utf-8")
  	stream.write(b"Content-Length: ")
  	stream.write(str(len(bytes_message)).encode("ascii"))
  	stream.write(b"\r\n\r\n")
  	stream.write(bytes_message)
  	stream.flush()

  
  

  autorest.python/packages/autorest.python/autorest/black/__init__.py

  Lines 31 to 39 in ba0cb0e

  	def process(self) -> bool:
  	# apply format_file on every file in the output folder
  	list(
  	map(
  	self.format_file,
  	[f for f in self.output_folder.glob("**/*") if f.is_file()],
  	)
  	)
  	return True