Lockdown query internals

Many things in query implementation are left public although they are very prone to creating insidious bugs if accessed externally. These are not proper extension points and should be made package local or provided strictly via SearchManagerImplementor.

• Move SearchManager.purge(Class) method to SearchManagerImplementor
• DefaultSearchWorkCreator should be moved to org.infinispan.query.backend and made package local
• TransactionalEventTransactionContext is not used, can be removed, and its non-tx counterpart (NoTransactionContext) no longer has to be public
• all public methods in QueryInterceptor must be reviewed and made package local ASAP