Reduce garbage-level of Drydock Allocator implementation
Summary:
Ref T9253. The Drydock allocator is very pseudocodey right now. Particularly, it was written before Blueprints were concrete.
Reorganize it to make its responsibilities and error handling behaviors more clear.
In particular, the Allocator does not manage locks. It's primarily trying to reject allocations which can not possibly work. Blueprints are responsible for locks. See some discussion in D10304.
NOTE: This code probably doesn't work as written, see future diffs.
Test Plan: See future diffs.
Reviewers: hach-que, chad
Reviewed By: hach-que, chad
Subscribers: cburroughs
Maniphest Tasks: T9253
Differential Revision: https://secure.phabricator.com/D14114