Add explicit open module declarations to models

MDSAL-752 added basis Automatic-Module-Name declarations. As the next step in JPMS integration, convert those stanzas to explicit module-info.javas.

While we want to discourage reflection, we also want to keep the maintenance to the  bare minimum required.

Covert all automatic modules to explicit open modules, as in:

open module org.opendaylight.yang.gen.ietf.inet.types.rfc6991 {
  // ...
} 

This provides a further tightening of the contract: all dependencies need to be explicitly declared, but reflection still works.