Introduce RecordArray
Summary:
This diff introduces `RecordArray`, a new `ArrayKind` which is backed by a `RecordData`-like storage. It also has a hash map to contain arbitrary field-value pairs that are not declared in the corresponding `RecordDesc`.
This diff also introduces `NewRecordArray` bytecode to create such arrays and the `Release` method, but stubs out all other `ArrayData` methods.
Reviewed By: paulbiss
Differential Revision:
D16381732
fbshipit-source-id:
ed0c6e64a3becd1a61600bfa93d4413c0b737cb1