Create a new header src/mongo/db/exec/expression/evaluate.h and define a namespace mongo::exec::expression with a set of functions

Value evaluate(const ExpressionDateFromParts& expr, const Document& root, Variables* variables)

one for each

• ExpressionDateFromParts
• ExpressionDateFromString
• ExpressionDateToParts
• ExpressionDateToString
• ExpressionDateDiff
• ExpressionDateAdd
• ExpressionDateSubtract
• ExpressionDateTrunc
• ExpressionTsSecond
• ExpressionTsIncrement
• ExpressionDayOfMonth
• ExpressionDayOfWeek
• ExpressionDayOfYear
• ExpressionHour
• ExpressionMillisecond
• ExpressionMinute
• ExpressionMonth
• ExpressionSecond
• ExpressionWeek
• ExpressionIsoWeekYear
• ExpressionIsoDayOfWeek
• ExpressionIsoWeek
• ExpressionYear

The body of the functions will be in a src/mongo/db/exec/expression/evaluate_date.cpp and will be taken from the evaluate() method, and the evaluate() method will be changed so that it calls the new method.