The number of elements the buffer can hold.
Capacity can not be set lower than DynamicBuffer<T0>.Length - this will raise an exception.
If Capacity grows greater than the internal capacity of the DynamicBuffer, memory external to the DynamicBuffer will be allocated.
If Capacity shrinks to the internal capacity of the DynamicBuffer or smaller, memory external to the DynamicBuffer will be freed.
No effort is made to avoid costly reallocations when Capacity changes slightly;
if Capacity is incremented by 1, an array 1 element bigger is allocated.