ConnectionFileDescriptor needs a different implementation on Windows and non-Windows platforms due to some fundamental differences. This patch moves source\Core\ConnectionFileDescriptor.cpp to source\Core\posix\ConnectionFileDescriptorPosix.cpp, and similarly for the corresponding header file. Then, the original ConnectionFileDescriptor.h is replaced with a new implementation that includes the platform specific header file.
Currently this patch does not actually implement Windows' version of ConnectionFileDescriptor. It only makes the organizational changes necessary for this to happen in a subsequent patch. As such, with this patch, Windows will actually be compiling source\Core\posix\ConnectionFileDescriptor.cpp. When the windows version of CFD goes in, the CMake will be updated accordingly to compile the windows CFD.
This patch contains no functional changes, only code move.