Document methods relative to projection

[Selene-Amanita]

Following https://github.com/bevyengine/bevy/issues/8492, a bunch of methods were renamed, it basically erased a lot of references to "projection" and replaced them with "clip". I didn't see this PR until after it happened, but I find the documentation (not the migration guide) surrounding it a bit lacking (not saying it's the fault/responsibility of the PR/its author, some of it was also the case before):

• I'm not sure it's clarified anywhere what is a "clip". I assume it's the space/box where stuff end up after the projection just before being rendered, but having next to no knowledge about rendering but knowledge in mathematics, "projection" is a much more understandable term for me and I don't think I'm the only one, it would be nice to have references to it in the comments of methods with "clip" in their name, like https://github.com/bevyengine/bevy/issues/8492 suggested, and/or have a definition of "clip" somewhere
• None of the methods of the trait CameraProjection have comments
• The documentation of the methods of the struct Frustum talk about clip_from_world. I assume it is referring to the method that comes from ExtractedView, but it is not clear (I know rustdoc doesn't help with not being able to reference stuff not from dependencies :( but still it could help to say it comes from ExtractedView and/or explain a bit what that method gives
• ExtractedView and ViewUniform aren't documented. We don't know where they're from (I assume ExtractedView is added as a component to the camera but not from Camera3dBundle?) or their purpose. Even if it's an internal thing, a brief description might help, especially since the Frustum's doc references it.
• Other types referenced in this PR are not documented like MeshTransform

Even if those things wouldn't matter much for someone that just codes a simple game, it might matter to plugin writers and people who want to understand how the rendering side of Bevy works.

[JMS55]

https://gpuweb.github.io/gpuweb/#clip-space-coordinates

[Selene-Amanita]

Thanks, that's what I thought it was.

I still think it should be explained in Bevy's doc though (and that you get from world space to clip space using the projection), or at the very least link to this doc, even though I find it a bit not super clear for people who aren't familiar with rendering stuff.

I'm not saying Bevy's doc should be a course on rendering, but I do think it should try to explain what's going on without necessarily going into details.