DERBY-6169: Reduce visibility of classes and methods under impl/sql

- Change visibility of all classes generated from sqlgrammar.jj to
  package protected.

- Make CompilerContextImpl.getParameterTypes() package protected since
  it's never called from outside the package.
DERBY-6169: Reduce visibility of classes and methods under impl/sql

- Make all fields of CreateViewNode private.

- Take a defensive copy in CreateViewNode.getProviderInfo() to prevent
  accidental modification by the caller.
DERBY-6169: Reduce visibility of classes and methods under impl/sql

Remove two unused methods in the TriggerExecutionContext interface,
and their implementations in InternalTriggerExecutionContext. This
also made it possible to remove some fields that were only used by the
removed methods, and also corresponding fields and parameters in
neighbour classes.