Implement accurate size storage for Windows _msize and _recalloc #786

With snmalloc we can provide a custom meta-data per object that is attached to the standard snmalloc meta-data such as free lists.

We could use this feature to store a single bit per object. The bit being set means the allocation does not consume the whole allocated space. The last byte then represents how much space is not being used by the allocation, i.e. 17 byte allocation, would have the last byte as 15 (32 - 17) and the bit would be set, whereas a 32 byte allocation would not have the bit set.