Some `IO::FileDescriptor` methods are implemented in `Crystal::System::File`

[HertzDevil]

flowchart BT
File --> IO::FileDescriptor
File --> Crystal::System::File
IO::FileDescriptor --> Crystal::System::FileDescriptor

These methods of IO::FileDescriptor are implemented in Crystal::System::File instead of Crystal::System::FileDescriptor:

• #fsync -> #system_fsync
• #flock_shared -> #system_flock_shared
• #flock_exclusive -> #system_flock_exclusive
• #flock_unlock -> #system_flock_unlock

Thus it is always a compilation error to call them on IO::FileDescriptors that aren't Files:

STDOUT.fsync            # Error: undefined method 'system_fsync' for IO::FileDescriptor
IO.pipe[0].flock_shared # Error: undefined method 'system_flock_shared' for IO::FileDescriptor

Either the methods in IO::FileDescriptor should be moved down to File, or the #system_ implementations should be moved to Crystal::System::FileDescriptor.