ntdll: Define a generic file information structure to allow supporting multiple info classes in NtQueryDirectoryFile.

The pointer address may set by the type unmarshalling function and
therefore will not be base_ptr_val. This value is the value at
*pPointer and is what needs to be retrieved during subsequent
unmarshalling of the same function.

Byref arguments should only be passed in the rgVarRef array, not in
arg array. Copy the value into the rgVarRef array before calling the
remote function to ensure that memory isn't allocated for the byref
pointers during unmarshalling.