Box ValidationError

[Rua]

Changelog:

Changes to errors:
- - `VulkanError` is renamed to `RuntimeError`.
- - Added new types `ValidationError` and `VulkanError` (enum of `ValidationError` + `RuntimeError`) to return errors from any function. Some existing functions have been converted to use these types, others will follow later.
+ - Added new types `ValidationError` and `Validated` (enum of `ValidationError` + something else) to return errors from any function. Some existing functions have been converted to use these types, others will follow later.

Fixes #2251. I've also un-renamed RuntimeError back to VulkanError, as I wasn't quite happy with that change in the end. I made the combo enum generic, so that it can be used for error types other than VulkanError.

[marc0246]

Really there should be a blanket impl

impl<E> From<E> for Validated<E> { ... }

I feel like.

[Rua]

I tried that, but it conflicts with the From<ValidationError> impl.

[marc0246]

I see, thanks.