Allow redeclaring typeattributes

Allows partners to add a new attribute definition to their public
policy without causing a compatibility failure with the AOSP system
image.

Bug: 67092827
Bug: 37915794
Test: build and boot aosp_sailfish with a new type declared in public
    policy.

Change-Id: I3899065affb6806ae9080e1a7dfa5a6f368370f0