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

- Make all fields of CreateViewNode and BasicProviderInfo private.

- Make BasicProviderInfo's constructor package private.

- Make CreateViewNode.getProviderInfo() return an immutable list
  instead of the actual array to prevent accidental modification by
  the caller.

git-svn-id: https://svn.apache.org/repos/asf/db/derby/code/trunk@1477476 13f79535-47bb-0310-9956-ffa450edef68