Swift TFramedTransport does not work using present code

These are TFrameTransport related issues from THRIFT-5125.

1. TFramedTransport.flush is not called anywhere; therefore, the message is never sent. outProtocol.transport.flush should be added to generated processors after outProtocol.writeMessageEnd, and also after writeException.
2. TFramedTransport.remainingBytes are not reset anywhere, thus the header of second and further messages are not processed properly
3. TFramedTransport.flush incorrectly checks if buffer >= headerSize (got there by incorrectly porting code COCOA lib)
4. TFramedTransport does not read the whole message from the underlaying transport at once (that I understand is the whole point of TFramedTransport)

Notes:

• 1. needs compiler changes

PR: https://github.com/apache/thrift/pull/2047