[SEDONA 710] Rename Geostats SQL classes to generic name; merge UdfRegistrator into AbstractCatalog

[james-willis]

Did you read the Contributor Guide?

• Yes, I have read the Contributor Rules and Contributor Development Guide

Is this PR related to a JIRA ticket?

• Yes, the URL of the associated JIRA ticket is https://issues.apache.org/jira/browse/SEDONA-710. The PR name follows the format [SEDONA-XXX] my subject.

What changes were proposed in this PR?

• Rename all the classes related to Geostats SQL to have names related to their functionality - creating custom physical nodes
• Create Expression Subclasses for both RDD and Dataframe based Physical Functions
• Merge the UDFRegistrator functionality into the AbstractCatalog so that users subclassing it get bundled functionality for adding their functions to the spark session.

How was this patch tested?

Unit Tests cover these refactors

Did this PR include necessary documentation updates?

• Yes, I have updated the documentation.

PhysicalFunction and DataFramePhysicalFunction have docstrings to help users of them