[Cosmos FTS] Expand full text search testing coverage

The initial release of full text search covers some good few queries to showcase the new results and work that can be done by the client and the service, but fails to account for many other scenarios that we should also cover. Would like to use this issue to track adding tests that:

- target individual physical partitions via partition-key
- target individual physical partitions via query plan using where clause
- real cross partition queries, where items are split across more than one physical partition
- partition split tests while performing these long-running queries
- tests using hierarchical partition keys
- tests covering the new countIf aggregate that was introduced
- tests covering split handling
To ensure this, we would ideally have a few logical partitions with ~100 docs in order to ensure that our matrix covers enough scenarios to make sure that any regressions or improvements are found quickly.

Follow-up to [42885](https://github.com/Azure/azure-sdk-for-java/pull/42885)