[sgen] Tweak internal class allocator sizes to add highly used on

[sgen] Tweak internal class allocator sizes to add highly used on

We observed on multiples benchmarks that most internal allocations are for 8, 16, 296 (32bits), 328 (64bits), 504 (32bits) and 1016 (64bits) bytes of memory. To minimize waste, we added these memory sizes to the default allocator sizes.