Introduce shader examples that don't use high level rendering apis

[IceSentry]

Objective

Most of the shader examples use the Material trait and the few remaining ones that don't use it might be updated in the future to either use that or some other high level rendering api.

We need an example that showcases a manual implementation for drawing a basic mesh without any high level apis.

There should also be an example showcasing a manual implementation of AsBindGroup.

These examples should be clearly used to showcase those lower level features and not be updated to higher level apis in the future.

Notes

Discord dicussion: https://discord.com/channels/691052431525675048/743663924229963868/1014539753854615662

[Vrixyz]

I might be interested in tackling that, but I'm open to suggestions for an exact behaviour to implement in the new example.

[IceSentry]

I think the example itself should be really simple. Nothing more complicated than the current shader_material example. The important part is that it showcases the mid-level rendering apis explicitly. Personally, I was planning on pretty much just writing the shader_material example but without using a Material. I just didn't have time yet.

[Vrixyz]

That sounds like re-establishing a previous iteration of that example (as a new lower level example): https://github.com/bevyengine/bevy/blob/adb3ad399cf092110b2d69f7dc189abc0ebc9f80/examples/shader/shader_material.rs should give a good base

[IceSentry]

Yeah, something like that would be a decent starting point. I think the important part would be having a lot of comment explaining what is going on.