Make arrays exportable only when their inner type is exportable

[lilizoey]

I also added a separate private function under the Export trait for some doctests. I wasn't entirely sure it made sense to put them in the Export trait's docs since they only really exist to test that compilation fails in certain scenarios and it might be a bit weird to just have a bunch of wrong examples.

fixes #870

[GodotRust]

API docs are being generated and will be shortly available at: https://godot-rust.github.io/docs/gdext/pr-875

[lilizoey]

i just realized, in some sense this is technically semver breaking as in code which used to compile now fails. but in another sense, any code that would be broken should hit #870 and thus panic on startup. idk what this counts as

[Bromeon]

Thanks!

It looks like doctests are also run for private functions, so export_doctests should be good! Could you maybe check if the compile_fail doctest still succeeds if the code actually compiles?

[Bromeon]

Suggested change

	impl<T: ArrayElement> Export for Array<T>
	where
	T: Export,
	impl<T> Export for Array<T>
	where
	T: ArrayElement + Export,

[lilizoey]

Thanks!

It looks like doctests are also run for private functions, so export_doctests should be good! Could you maybe check if the compile_fail doctest still succeeds if the code actually compiles?

if i comment out the relevant bounds to make both of the exports compile, then the compile_fail doctests do fail.

[Bromeon]

Thanks!