Break down SweepVMSpecific to smaller packets and move the packets to Release

[qinsoon]

We currently create a packet SweepVMSpecific that sweeps malloc'd arrays, stack pools, and weak references for all the threads, and the packet was put to the Compact bucket.

We should break down the work packet into smaller packets, SweepMallocedArrays, SweepStackPools and SweepWeakReferences for each thread. And we should schedule the packets to the Release bucket.