Differential Revision: D61675022

…er (facebook#1504)

Summary:
Pull Request resolved: facebook#1504

Large segment needs to be backed by a large storage size.
StorageProvider currently always allocate fixed size of storage
determined by HERMESVM_LOG_HEAP_SEGMENT_SIZE.

This diffs adds support of allocating larger storage with below
changes:
1. `newStorage()` and `deleteStorage()` takes additional `sz` parameter.
2. For `MallocStorageProvider` and `VMAllocateStorageProvider`, simply
change the previous fixed storage size to passed in `sz`.
3. For `ContiguousVAStorageProvider`, use a BitVector to manage
allocations and deallocations. This can be improved later if we observe
fragmentations.

The support of enabling different sizes of heap segment will be added
later.

Differential Revision: D61676721