Improve package resolution APIs on CelerityResourceMap

Summary:
Ref T4222. A few diffs from now, CelerityResourceMap will have a CelerityResources inside of it:

• Rename resolvePackage() to getResourceNamesForPackageHash(). This isn't a functional change, it's just making it clear what it does.
• Add getResourceDataForName(), to push details about storage into CelerityResources.

Test Plan: Reloaded a bunch of pages, rebuilt map.

Reviewers: btrahan, hach-que

Reviewed By: hach-que

CC: aran

Maniphest Tasks: T4222

Differential Revision: https://secure.phabricator.com/D7869