handle out-of-order dex sequence when unpacking xzs dexen
handle out-of-order dex sequence when unpacking xzs dexen

Summary: pre-dexed xzs build can produce dex files that are not in sequentially increasing order, extract the order from the metadata so that the blob is split correctly

Reviewed By: bertmaher

Differential Revision: D3833595

fbshipit-source-id: 2eb028e70d957427fe91e1a760dc43c48ce08234

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