[PATCH 2/3] core-local array type conversions

[PATCH 2/3] core-local array type conversions

Summary:
try to clean up the type conversions and hope it passes on windows.

one interesting thing I learned is that bitshift operations are special: in `x << y`, the result type depends only on the type of `x`, unlike most arithmetic operations where the result type depends on both operands' types.
Closes https://github.com/facebook/rocksdb/pull/2277

Differential Revision: D5050145

Pulled By: ajkr

fbshipit-source-id: f3309e77526ac9612c632bf93a62d99757af9a29
(cherry picked from commit bbe9ee7dd4a542b191ace521ca13b4bdb063008b)

Gbp-Pq: Name 0002-core-local-array-type-conversions.patch