Introduce EntityInfo class

Wrap the entity info array structure in an object,
for type safety and conveniant access.

Note that the individual entity records are still plain
array structures, for speed and memory efficiency.

Change-Id: I859f581c59d7ff5dd7d282e895174dd634773337
Fix missing/unused private properties in DirectSqlStore

* Add missing 'useLegacyUsageIndex' class property.
* Remove unused 'changesDatabase' class property.
* Add null to class property docs that can be null.
* Also fixes a variable name in MockClientStore that's to specific.

Change-Id: If4f0fa208800f69fa4e30a7b33dd2e04c724fe08
Merge "Introduce EntityInfo class"
Merge "Fix missing/unused private properties in DirectSqlStore"