Add support for range based loops for Array

[tomfull123]

Fixes #1710
This PR adds support for range based loops for the TypedArray class.
Allowing syntax such as:

TypedArray<int> elements;
for (const auto& e : elements) {}

I wanted to get proper type inference for the element, but I had issues getting the Variant type to cast properly.

[dsnopek]

Thanks!

However, one of godot-cpp's core design goals is to be compatible with Godot's internal APIs, and this differs a little bit from them:

• I don't think we should publicly expose ptr() or ptrw() because Array/TypedArray don't have them in Godot
• These iterators should be on Array rather than TypedArray, because that's where they are in Godot, and that would also allow folks to use range-based loops an Arrays, which would be nice

[tomfull123]

Changed the PR to now add the iterator to Array instead of TypedArray, I can make the ptr() and ptrw() methods private, but they are public in the PackedArray classes, so it would be consistent with those, but maybe its better for them to have those methods private too, what do you think? @dsnopek

I think ptr() and ptrw() should be made private in all the PackedArray classes too, to match Godot, I can put in a PR for that too.

[dsnopek]

Thanks!

Changed the PR to now add the iterator to Array instead of TypedArray, I can make the ptr() and ptrw() methods private, but they are public in the PackedArray classes, so it would be consistent with those, but maybe its better for them to have those methods private too, what do you think?

The goal isn't to be internally consistent among the classes in godot-cpp, but to be consistent with the API of Godot.

In Godot, the PackedArray classes have public ptr() and ptrw() methods, but Array/TypedArray do not, so we should do the same in godot-cpp. If we wanted to have those methods on Array/TypedArray, we'd need to make a PR to add them to Godot first.

Also, lots of extensions are already using ptr() and ptrw() on the PackedArray classes (including some I maintain :-)) so we really couldn't remove them now anyway

[tomfull123]

@dsnopek cool, the Array's ptr() and ptrw() methods are now private

[tomfull123]

Is this PR waiting on anything? @dsnopek do you have any other concerns?

[dsnopek]

Thanks, this is looking good to me now!

Only one last thing - this needs to be squashed to a single commit per Godot's git workflow: https://docs.godotengine.org/en/latest/contributing/workflow/pr_workflow.html#the-interactive-rebase

(This applies to all your PRs, actually - sorry that I didn't notice earlier that you were making multiple commits)

[tomfull123]

Ahh no worries, I should have read the PR guidelines more thoroughly, should be good to go now