Objective

• Another step towards render recovery after RenderCreation refactor #22714 and cleanup bevy_render/lib.rs #16481
• We need RenderResource unpacking to be reusable from a non-app context

Solution

• Make it take main and render worlds as input
• Use subapp destructure to get mutable access to both worlds simultaneously
• Move it to live next to the struct def
• Document
• Also move shader library loads up to build because theres no reason for them to be in finish

Testing

• 3d_scene runs

Note: reviewing commit by commit is easier, when a large block moves its just copy paste