R1:99b4941c9ad3

Conpherence - use some handle pools for Durable column perf

Summary:
Ref T7708.

This changes things to $viewer->loadHandles where applicable in the durable column render stack. I saw some big wins on my test data like 34 queries => 24 queries on a newly created room as my default thread.

For my test data, the next big perf win would be to change how remarkup rendering works and try to multiload all objects of a certain type in one shot.
e.g. `PhabricatorEmbedFileRemarkupRule` implements `loadObjects` as…