Unlike to `lookup_or_default` accessor methods of `Map` or attribute provider class,
`Span::get` is not so explicit and self described to be used with default value.
Other one issue was is that result is by value. But this is not the main reason to
delete this method. And although this can be fixed by reference, this is still not
such good to just have method to check index and return something.
Pull Request: https://projects.blender.org/blender/blender/pulls/122425
bea8825446