Extract extract to bevy_extract

[Zeophlite]

Objective

• Make the extract infra is reusable for non-rendering crates (this is final PR in bevy_extract tracking #24483 )

Solution

• Create bevy_extract crate, containing "extract/sync" stuff from bevy_render

Please review commit-by-commit:

• 779f73e756 - Create bevy_extract crate skeleton
• 4accfeef81 - Move sync/extract files from bevy_render to bevy_extract
• b9cbb446e9 - Move ExtractComponent , ExtractResource derive macros
• 79745aa880 - Migrate code to be compatible (fix imports, remove L = RenderApp default, add compat types in bevy_render, etc.)
• c491f11e35 - Fix docs so links work
• 333fead16d - Rework docs to remove most of render from bevy_extract
• eec1fd4dcf - CI fixes

Simplified by #23377

Testing

• CI
• cargo run --example animated_mesh

[github-actions]

You added a new feature but didn't update the readme. Please run cargo run -p build-templated-pages -- update features to update it, and commit the file change.

[atlv24]

This is skipping a few steps but its roughly the goal. We need a few preparatory steps, each of these should be its own PR:

• The resource marker change to allow orphan rule circumvention on resource impls
• Making ExtractPlugin take the app label (RenderApp) as generic parameter instead of hardcode
• Making ExtractPlugin take a schedule to run and having its own internal extract schedule which handles the pre and post actions, running the user provided systemset/schedule in the middle
• improving the macro situation to hide existing complexity of implementations
• collapse manual implementations of extract into derive macro call or whatever
• Introducing an AppLabel marker to Extract impls to specify that they are RenderApp extract impls and tuck it away neatly into the macro
• Rename test terminology in extract_plugin.rs to not reference rendering
• finally, this PR

[Zeophlite]

New version, extending https://github.com/atlv24/bevy/tree/ad/extract-label ( #22855 )

cargo run --example animated_mesh works now, but at reduced DX (Need to pass RenderApp around a bunch still)

[Based-A]

Overall the documentation substitutions are good, there's just a couple of points I have around using "processing" as a substitute for "rendering". "Processing" feels too much like a black box, and even though you don't want to nail it down to a specific use case or example, it can still be confusing as to what "processing" actually means for the whole thing. Although some uses of it are fine, especially when the thing being talked about is detailed as a defined part of the "processor"/"processing".

[Zeophlite]

@Based-A I've updated based on your feedback, please have another look

[Based-A]

Much better, comments look good from my perspective.

[kfc35]

my comments are mostly to do with documentation

i can approve after theyre addressed

[kfc35]

This probably needs to be fleshed out a little bit more

Suggested change

	//! This crate is about everything concerning extract.
	//! This crate provides a way to extract component information from
	//! an app’s main world into a sub world.

I think at least mentioning that the ExtractPlugin is how you mainly set it up, and maybe that extract/sync components to specify exactly how component data may be transformed from the main world to the sub world would also be helpful.

Just mentioning this documentation comment in general since it seems the extract infrastructure isn’t used uniformly by all bevy rendering devs and a little documentation can go a long way to getting this adopted more widely across the rendering codebase

[Zeophlite]

Okay I've had a go at some crate docs, please have a look

[kfc35]

Nice job! Hope it gets merged without a hitch 👍

[kfc35]

I think the only additional docs I might add at the top level are about the difference between the terms extract and sync and some basics on how to use the sync tools but that can be a quick followup if desired