perf: improve performance of Bavet indexing

[triceo]

Refactors indexing in Bavet so that:

• IndexKeys (formerly IndexProperties) become bimorphic as opposed to megamorphic, enabling all kinds of JVM optimizations.
• Many instances of IndexKeys are no longer created as they were unnecessary. (Case in point: SingleIndexProperties is gone, without replacement.)
• There is less indirection in the nodes.
• Naming of keys, functions and mappings is standardized across the board.

In the score director benchmarks, these changes show throughput improvements of up to 10 %, with GC pressure reduced by up to 40 %.

[triceo]

Please review after we're done with the release, @zepfred.
You have already seen most of these changes before, in the commit that was originally reverted.

[sonarqubecloud]

Quality Gate passed

Issues
1 New issue
0 Accepted issues

Measures
0 Security Hotspots
71.7% Coverage on New Code
1.7% Duplication on New Code

See analysis details on SonarQube Cloud

[zepfred]

LGTM!