[Bind] Add int overloads to buffer size (IntPtr) parameters

As a convenience, int overloads are provided for IntPtr size
parameters (corresponding to BufferSize or size_t). In the vast
majority of cases, a 32bit int is sufficient for buffer sizes,
so these overloads avoid the necessity of annoying (IntPtr) casts.

If more than 2^31-1 elements are required, the IntPtr overloads
remain available. (As always, this requires a 64bit runtime
environment.)