R1:b51a859636ac

Allow diffusion.filecontentquery to load data for arbitrarily large files

Summary:
Fixes T10186. After D14970, `diffusion.filecontentquery` puts the content in a file and returns the file PHID.

However, it does this in a way that doesn't go through the chunking engine, so it will fail for files larger than the chunk threshold (generally, 8MB).

Instead, stream the file from the underlying command directly into chunked storage.

Test Plan:
- Made a commit including a really big file: https://github.