Probe the new Python bindings Map key "comparer" & CEL expression based Map key "comparer"

[grecinto]

Add more automated tests to probe the above listed features of the new Python bindings.

[grecinto]

CEL expression support was put off in the future. Perhaps when SOP supports UDF on per field of MapKey comparison. BUT the IndexSpecification based approach is solid for release. Allows very easy definition of which fields of the map key is for use in comparer, to establish feature similarity of "index definitions" in RDBMS.