Add support for initializer_list to TypedArray

[tomfull123]

This PR adds support for initializer_list syntax, allowing TypedArrays to be assigned more easily, with syntax such as: TypedArray<int> x = { 1, 2, 3 };

Its a nice to have feature that I've found missing while developing gdextensions, I'm also writing a gdscript to gdextension transpiler and this syntax would help to make that possible.

[Ivorforce]

Hi, and welcome!
This is a welcome contribution - initializer list construction is useful indeed.
In this case, it's relevant to know that godot-cpp has a design goal to stay close to Godot code as closely as possible. In some circumstances, this means not (yet?) adding features that are not in Godot upstream.

initializer_list construction for TypedArray is a bit of an outlier though, perhaps. While it's not in Godot yet, there are three (!) open pull requests that attempt to add it ([1], [2], [3]). It's probably only a matter of time till the Godot codebase merges one that adds them... But arguably we might wait to merge this PR until then.

[tomfull123]

Yeah I saw those PRs a while back, I wasn't sure if it was a requirement to have it in Godot first, either way, I don't mind waiting, at least this PR will be ready to go when we finally get the feature in the Godot codebase.

[dsnopek]

Thanks!

However, I think we should wait for Godot to merge one of the upstream PRs before merging this one