Use file.allocate to upload large files from arc diff

Summary: Fixes T8259. Depends on D13016. Use modern logic to support large file uploads.

Test Plan:

• Diffed with some images, saw them show up in the diff.
• Diffed with a 12MB binary, saw it upload in chunks.

Reviewers: btrahan

Reviewed By: btrahan

Subscribers: epriestley

Maniphest Tasks: T8259

Differential Revision: https://secure.phabricator.com/D13017