Allow serializers to use upper and/or lower case ids, as needed.

Since Lua code may perform lookups on serialized entities using hardcoded
lower case property IDs, we need to retain support for this when moving to
upper case IDs.

Change-Id: I76f220fd1fb7b31b06b04011c82cc460b3a087aa
Merge "Allow serializers to use upper and/or lower case ids, as needed."