Fix tuple equality with null values

[cmoesel]

Previously, if tuples had the same fields, and at least one field had a null value on one tuple and a non-null value on the other, then:

• if the null/non-null field came after a field with different values, it returned false (which is correct)
• if the null/non-null field came before a field with different values, it returned null (which is incorrect)

Now it will return the correct answer regardless of where the null/non-null field is.

NOTE: This PR does not fix npm audit issues or the codecov issue, as those have already been fixed in #326. As a result, this should be merged after #326.

Submitter:

• This pull request describes why these changes were made
• Code diff has been done and been reviewed (it does not contain: additional white space, not applicable code changes, debug statements, etc.)
• Tests are included and test edge cases
• Tests have been run locally and pass
• Code coverage has not gone down and all code touched or added is covered.
• Code passes lint and prettier (hint: use npm run test:plus to run tests, lint, and prettier)
• All dependent libraries are appropriately updated or have a corresponding PR related to this change - N/A
• cql4browsers.js built with npm run build:browserify if source changed.

Reviewer:

Name:

• Code is maintainable and reusable, reuses existing code and infrastructure where appropriate, and accomplishes the task’s purpose
• The tests appropriately test the new code, including edge cases
• You have tried to break the code

[codecov-commenter]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 87.05%. Comparing base (12a8ce0) to head (2f61fef).

Additional details and impacted files

@@           Coverage Diff           @@
##           master     #327   +/-   ##
=======================================
  Coverage   87.04%   87.05%           
=======================================
  Files          52       52           
  Lines        4517     4518    +1     
  Branches     1273     1273           
=======================================
+ Hits         3932     3933    +1     
  Misses        377      377           
  Partials      208      208           

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