LUCY-295 Adapt for changed return type of Vec_Get_Size

[rectang]

The Clownfish API Vec_Get_Size has changed from returning uint32_t to returning size_t. Adapt Lucy for the effect of this change.

This branch is broken up into commits according to the kind of remedy that was applied at each site, and the associated difficulty of proofing the change.

[nwellnhof]

I see that you avoided any type changes to instance variables or method parameters and return values. So what we have now is a couple of explicit but still unchecked casts from size_t to uint32_t. This shouldn't matter in practice, but part of me prefers to convert all these variables and parameters to size_t, including I32Array and BitVector. Also, when serializing a size_t as 32-bit value, 100% correct code should check for overflow like

size_t size = Vec_Get_Size(vector);
if (size > UINT32_MAX) {
    THROW(...);
}
OutStream_Write_U32(outstream, (uint32_t)size);

(Or check before adding elements to such arrays.)

OTOH, this seems silly for things like the number of PolyQuery children, document fields, or sort rules.

[rectang]

I agree with making I32Array and BitVector use size_t internally to match the other types. Once they are converted, it will make sense to go back and fix the unchecked-but-explicit casts.