Split large tests into multiple smaller tests

If large tests fail, it can be complicated to find the origin of the issue.

For example `JanusGraphTest.testSchemaTypes`: This test contains tests for multiple different types: Float, String, Object, ... .
Further, this tests also contains:
* valid schema creation tests
* invalid schema creation tests
* valid insertion tests
* invalid insertion tests

Locate JanusGraphTest and inspect testSchemaTypes, which currently covers multiple schema types and valid or invalid schema creation and insertion. Split the coverage into smaller independent tests, then run the relevant JanusGraph tests and confirm failures identify a specific type or operation.

Written by the indexing model from the issue text.