Update base for Update on "Add segment_data_size to extended header"

Store the segment data size. Allows us to calculate the total PTE file size and error out if the full PTE file was not downloaded.

Next diff: check file size at runtime.

Differential Revision: [D81829663](https://our.internmc.facebook.com/intern/diff/D81829663/)

[ghstack-poisoned]

Author: lucylq