Change CreatePipe to use SafeFileHandle instead of SafeObjectHandle

[ZoeyR]

The CreatePipe method should output SafeFileHandles intead of SafeObjectHandles. By outputting SafeFileHandle directly it makes it easier to wrap these up in FileReader and FileWriter classes.

[qmfrederik]

There's a lot of Kernel32 which interop with files. Basically every first argument to a Kernel32 method which is named hFile or hDevice should be a SafeFileHandle instead.

It makes a lot of sense to change them all. @AArnott thoughts?

[blakegordon]

I had similar thoughts to the OP's, only CreateFile was the API I cared about. Help me understand the thinking in returning SafeObjectHandle? None of the .NET FileStream constructors know what to do with that, but maybe you had a different .NET API in mind to interact with SafeObjectHandles?

[AArnott]

Probably not enough care in choosing it. I could see us unifying this.