Add policy style '@'/'!' rules to prop protections

A value of '@' will always allow the corresponding operation for a
property, and '!' will always disallow the operation.

Related to blueprint api-v2-property-protection

DocImpact

Change-Id: I1196a58a6f97cd0856bf97463386776a00359a49
Merge "Add policy style '@'/'!' rules to prop protections"