Fix bug to make --clear-output-folder work (solution 1)

[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

[msyyc]

I don't find effective way to flush the buffer into disk in time. How about changing another way: if we format the file content before write, we can avoid the annoying problem. What's more, we reduce black plugin to make the flow shorter which is cleaner.

[msyyc]

and it would be breaking to make users not be able to turn off black
@iscai-msft users can still turn off black: https://github.com/Azure/autorest.python/pull/1410/files#r961250499 and https://github.com/Azure/autorest.python/pull/1410/files#r961250788 which will not bring breaking change. And multiapi/multiclient can also use black after this PR.

[msyyc]

users can still turn off black (cadl-python)

[iscai-msft]

@msyyc is there really no way to keep black as a separate plugin? Conceptually it really is a plugin, so it makes the code a lot less clean by adding black throughout the different plugins. I can take a look in a bit to see if it can't be done, but I think there should be a way to fix the current plugin we have, instead of doing this refactoring

[msyyc]

@iscai-msft It is nice if you can take a look. stream.flush can't ensure flush to disk before black read it. The memory inconsistency is always hard to handle so I think the best way is to bypass it completely. Plugin black may be clean but it can't work for multiapi/multiclient. In one word, my fix pr is just one of possible ways but I think it can resolve the problem for good.
nit: the bug seriously influence our release for mgmt SDK so I hope it can be resolved asap.
add @lmazuel for awareness.

[msyyc]

users can still turn off black(autorest)

[weidongxu-microsoft]

What's the reason that many samples/tests files get updated? Is it because previously black did not apply to them due to the bug?

[msyyc]

What's the reason that many samples/tests files get updated? Is it because previously black did not apply to them due to the bug?

Yeah. And with the fix, multiapi/multiclient can also enable black which is not permitted before.

[msyyc]

close for #1434