Update triangle example to use the task graph

[CptPotato]

Updates the triangle example to use the task graph.

The changes follow the deferred example. Colors were adjusted, as discussed on Discord.

[CptPotato]

I kept the previous comments where applicable, but haven't added any new ones. So this still needs another pass in terms of documentation.

But other than comments, this one is ready for review.

[CptPotato]

I first tried to use target: Id<Image> here instead of directly referring to the swapchain. This seemed cleaner, since the triangle task technically doesn't need to know that the target is a swapchain.

But didn't get it to work after some trial and error. Not sure if this is possible atm.

[marc0246]

<Id<Swapchain>>::current_image_id just casts the type parameter if you look at the implementation. This is but one of the reasons that the type parameter doesn't make sense.

[marc0246]

Do you think rgb(251, 113, 133) looks the best for the trongle? 🤔

[marc0246]

First thing that jumps out is that the TriangleTask struct and its impls should come after all the App and RenderContext structs and impls. We always order free-standing functions as well as structs and their impls from outermost to innermost. I suggest you fix this ASAP because it matters a lot for when you write the comments.