* Handling of #REF! Errors in Subtotal, and More
This PR derives from, and supersedes, PR #2870, submitted by @ndench. The problem reported in the original is that SUBTOTAL does not handle #REF! errors in its arguments properly; however, my investigation has enlarged the scope.
The main problem is in Calculation, and it has a simple fix. When the calculation engine finds a reference to an uninitialized cell, it uses `null` as the value. This is appropriate when the cell belongs to a defined sheet; however, for an undefined sheet, #REF! is more appropriate.
With that fix in place, SUBTOTAL still needs a small fix of its own. It tries to parse its cell reference arguments into an array, but, if the reference does not match the expected format (as #REF! will not), this results in referencing undefined array indexes, with attendant messages. That assignment is changed to be more flexible, eliminating the problem and the messages.
Those 2 fixes are sufficient to ensure that the original problem is resolved. It also resolves a similar problem with some other functions (e.g. SUM). However, it does not resolve it for all functions. Or, to be more particular, many functions will return #VALUE! rather than #REF! if this arises, and the same is true for other errors in the function arguments, e.g. #DIV/0!. This PR does not attempt to address all functions; I need to think of a systematic way to pursue that. However, at least for most MathTrig functions, which validate their arguments using a common method, it is relatively easy to get the function to propagate the proper error result.
* Arrange Array The Way call_user_func_array Wants
Problem with Php8.0+ - array passed to call_user_func_array must have int keys before string keys, otherwise Php thinks we are passing positional parameters after keyword parameters.
7 other functions use flattenArrayIndexed, but Subtotal is the only one which uses that result to subsequently pass arguments to call_user_func_array. So the others should not require a change. A specific test is added for SUM to validate that conclusion.
* Change Needed for Hidden Row Filter
Same as change made to Formula Args filter.
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