Support setting public attributes before object creation

[francois-normandin]

The use case is to inject attributes during the enumerateStaticDependencies callback, at a time when the SMO dependency might not be created yet. This feature would store attributes byValue until object creation where the attribute would be set in the pipeline just prior the onCreated callback.

[francois-normandin]

build 1.4.0.64 overwrites Identity in the newly created attributes. Fix is simple: merge attributes instead of overwiting.