Merge: Fix >= and <= operators for date queries

This adds two missing branches in the `getDateWhereClause` function and fixes an consistency in the `constructDateTimeWhereClauseForColumn` function.

# Focus

1. Don't let the whitespace changes confuse you.
2. The changes in `constructDateTimeWhereClauseForColumn` merely add an "OR value_ns IS NULL".
3. The changes in `getDataWhereClause` add an ELSEIF branch for each operator.