Add Prefix Sum method to numerical Arrays

[daviskyLV]

Currently, to calculate the prefix sum of a numerical array in GDscript you would have to do it manually via for loop. This is fine for smaller arrays, but for large arrays it would be preferable to have a built in solution, as it would be more performant.

The method could look something like this:
Array.prefix_sum(numerical_array, exclusive = false)
Since the regular Array type can hold Variant types, perhaps it would be better to limit this to only Packed[NumberType]Array?

I'm not well versed in C++ or Godot internals, but from my understanding it would be relatively easy to implement, as C++ provides the methods already: std::inclusive_scan and std::exclusive_scan.