Make Array/Packed*Array slice consistent

[nathanfranke]

Describe the project you are working on

godotengine/godot#35901

Note 1: All references in this proposal are after the changes in the above PR (e.g., end is exclusive).

Note 2: For those not familiar with it, Packed arrays are implemented as Vector internally, so whenever I say Vector I am referring to Packed*Array.

Describe the problem or limitation you are having in your project

Array.slice and Vector.slice behave differently

1. Array takes begin, end, step, deep, Vector takes only begin and end.
2. Array will never error unless step is invalid, while Vector fails if the indices are not -size() <= i < size().

Describe the feature / enhancement and how it helps to overcome the problem or limitation

1. Remove step.
2. All indices out of bounds will error: 0 <= i < size(), with the exception of -1 for end. I think this makes sense because:
   a) I find it unlikely that someone will pass -2 to mean the second to the last element, since that's kind of oddly specific.
   b) This way there can be a default value of -1.

Describe how your proposal will work, with code, pseudo-code, mock-ups, and/or diagrams

var arr := []
arr.push_back(0)
arr.push_back(1)
arr.push_back(2)
arr.push_back(3)

print(arr.slice(1, 3)) # [1, 2]
print(arr.slice(0, -1)) # [0, 1, 2, 3]
print(arr.slice(0, -2)) # ERROR

If this enhancement will not be used often, can it be worked around with a few lines of script?

Array and Vector are used often.

Is there a reason why this should be core and not an add-on in the asset library?

Array and Vector are part of core.

[nathanfranke]

Pretty much fixed as of godotengine/godot#35901

Only the end index can be negative. And there is still a step parameter, but it doesn't really hurt to keep it as of now.