Lucene cross class queries

[timw]

What does this PR do?

Port the SEARCH_CROSS Lucene cross class index search function from the enterprise agent codebase.

Motivation SEARCH_CROSS is described in the documentation for enterprise edition, but is not built/distributed with the open source based enterprise agent.

Additional Notes There's a minor hack (along the lines of the existing minor hack) to allow the LUCENE_CROSS_CLASS index to be created without triggering the manual index deprecation.

Checklist [x] I have run the build using mvn clean package command [x] My unit tests cover both failure and success scenarios

[timw]

We didn't end up using cross class indexes, so don't have any push to continue this work - happy for you to close the PR.