Make new storage and old starge seperate

This commit separates the new and old storage accessing code, so we can
ramp a flag to switch the storage used in java codegen from old to new.

This change doens't include switch the storage for exported mode. For
exported mode, it will still use DeviceConfig as the storage.

Bug: 368135182
Test: atest aconfig.test.java
Change-Id: I6e45d1ca98b3c7aeb1937669a8074805181903fe