Don't use Sweepable for APCLocalArray

Summary: Keep track of APCLocalArrays using a dedicated list in MemoryManager,
similar to how we track APC strings. This makes APCLocalArray not
use Sweepable, which devirtualizes it and reduces sizeof from 64 to 40.

Reviewed By: @jdelong

Differential Revision: D1669231

Signature: t1:1669231:1415548069:e617e85f2866d031f9dc313ccc69420d3d19f3ba