Add new flag ARRAY_FILTER_PACK_RESULT

[DanielEScherzer]

No description provided.

[DanielEScherzer]

Requested by someone at PHPTek and seemed pretty simple to implement
Our current documentation notes that

Array keys are preserved, and may result in gaps if the array was indexed. The result array can be reindexed using the array_values() function.

This would eliminate the need for an extra method call and improve performance

Plenty of existing code would use this: https://github.com/search?q=language%3Aphp%20-is%3Afork%20-is%3Aarchived%20%2F%5C%5C%3Farray_values%5C(%5Cs*%5C%5C%3Farray_filter%2F&type=code

let me know if an RFC is needed, not sure if this is small enough or not