[TF/XLA] Add stricter checks of buffer sizes within colocated buffer sets.

Note that there are already existing checks in BufferAllocation::AddAssignment
to ensure all buffers are no larger than the allocation. But colocated buffer
sets are used to handle forced aliasing, e.g. kWhile, kCall and kConditional,
which require all buffers to be identically sized.

PiperOrigin-RevId: 181565074