Bugfix: Fixes for f_file exposed by unit tests.

Bugfix: Fixes for f_file exposed by unit tests.

Restructure private_f_file_close() to be more consistent with the parameter ordering as is done with the rest of the project.

Have f_file_stream_close() not handle flush errors so that close is only to be called once.
The design of fclose() and close() state that even on error the descriptors are freed.
This means that file close doesn't fail, it always succeeds.
But the errors need to be propogated.
Ignore flush and always call close so that the behavior of never calling close twice can be guaranteed.
The private_f_file_close() will still
This also means that the stream and descriptor are to always be reset on close.

Return values need to be updated for several functions.

Rename f_file_stream_descriptor() to f_file_stream_open_descriptor() to make it clear that this is an open command.