ES|QL In operator test inconsistencies

[craigtaverner]

When investigating why the IN operator claims to support the new geogrid types, while the unit tests for it do not test these types, we found that some inconsistency was also found for datetime types, which are not on the types list, and yet there is explicit support for resolving these types. In addition there is no InErrorsTests to pair with InTests, so testing coverage is lacking.

We should:

• Add geo-grid types to the tests
• Figure out if datetime types are supported or not, and add them to the tests and types lists
• Add missing InErrorsTests and perhaps InSerializationTests
• Look for any further inconsistencies

[elasticsearchmachine]

Pinging @elastic/es-analytical-engine (Team:Analytics)