Documentation for the new renderer

[kurtkuehnert]

Objective

• Currently all information on the new renderer is scattered between Discord, Renderer Rework: Initial Merge Tracking Issue #2535, Bevy Render Rework: Initial Framing and Proof of Concept #2265 and Bevy Render Rework Round 2: SubGraphs, Views, and Shadows #2351.
• That makes it pretty hard to grasp all of the concepts, especially for people new to Bevy.
• We will probably want good documentation for 0.6 anyway so I've made a first attempt.

Solution

• Provide documentation for the new renderer so (new) developers can get started faster with switching to and/or extending it.

Questions

• How should the PRs be scoped? One giant one for the entire renderer, or one per module?

Any advice one adding code examples would be appreciated. :)

[mockersf]

could you try rebasing instead of doing a merge commit? it makes it very hard to review

[kurtkuehnert]

sry, this went terribly wrong :(. I rebased onto the current pipelined rendering locally, but this resulted in this mess. How can I revert those changes? @mockersf

[kurtkuehnert]

I think this it :).
I am probably done with this PR for now and it should be ready for review/merging.
I have not managed to document everything, most notably the module descriptions, buffers, shaders and views, pbr and the core pipeline.
University has started again so I won't have the time to finish those, but I can resolve merge conflicts if needed.

[alice-i-cecile]

Closed in favor of the rebased #3094.