The comparison operators offered by the comparison dropdown.
By default this property returns null and the dropdown filters the operators by the
value type: ordered types such as numeric types offer every ConditionComparison operator,
other types offer equality operators only. Override this property to supply your own list of operators;
an empty list behaves like null and falls back to the type-based defaults.
It is only relevant when Condition<T0>.DisplayComparisonDropdown is overridden to return
true.