Summary:
Cleans up `ReadableMapBuffer` APIs and migrates to use `std::vector` instead of raw pointer array.
Also uses `fbjni` utility to allocate the bytes instead of making manual JNI calls.
Changelog: [Internal]
Reviewed By: sammy-SC
Differential Revision: D33513027
fbshipit-source-id: afe7d320d12830503de4c9994117d849f0b25245