Update behavior of included operator

[JPercival]

• Resolves #1344
• The CQL spec states that nulls receive special handling for Lists and also states that included in is equivalent to includes for singleton values, so there's a bit of inconsistency there that needs to be addressed:
  • https://cql.hl7.org/09-b-cqlreference.html#included-in

    For the point overload, this operator is a synonym for the in operator, and will return null if the first argument is null, and false if the second argument is null.

  • https://cql.hl7.org/09-b-cqlreference.html#in-1

    If the first argument is null, the result is true if the list contains any null elements, and false otherwise. If the second argument is null, the result is false.

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Codecov Report

All modified and coverable lines are covered by tests :white_check_mark:

Project coverage is 63.14%. Comparing base (75801fe) to head (3118892).

Additional details and impacted files

```diff @@ Coverage Diff @@ ## master #1353 +/- ## ============================================ - Coverage 63.17% 63.14% -0.03% + Complexity 6132 6127 -5 ============================================ Files 468 468 Lines 25360 25358 -2 Branches 4720 4719 -1 ============================================ - Hits 16020 16013 -7 - Misses 7183 7184 +1 - Partials 2157 2161 +4 ```

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