R1:bb306b58d553

Introduce DifferentialChangesetQuery and remove loadHunks()

Summary: Ref T4045. Ref T5179. This removes all non-Query hunk loads.

Test Plan:
- Viewed revisions.
- Viewed standalone changesets.
- Viewed raw old/new files.
- Viewed vs diffs.
- Enabled inline comments in mail and sent some transactions with inlines.
- Called `differential.getrawdiff`.
- Grepped for `loadHunks()`.

Reviewers: btrahan

Reviewed By: btrahan

Subscribers: epriestley

Maniphest Tasks: T4045, T5179

Differential…