Extract extract to bevy_extract

[Zeophlite]

Objective

• Make the extract infra is reusable for non-rendering crates (see bevy_extract tracking #24483 )

Solution

• Follows Extract Extract prework #24423
• Create bevy_extract , containing "extract/sync" stuff from bevy_render

Reviewer notes: changes for this PR are listed below. Other commits are pre-requisties in the preceeding PRs. Please review commit-by-commit:

• 9e1b4bf894 - bevy_extract skeleton
• ea26d5e7a0 - Move to bevy_extract
• 2aefc2a70c - Move macro lib
• 8e6c218815 - Migrate
• 4dd4b933f7 - Fix docs
• 102020b6b6 - Rework docs to remove most of render from bevy_extract

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)

[Zeophlite]

I was hoping to use the below, but it's an unstable feature

pub trait ExtractComponent<F : 'static + Send + Sync = ()> = ExtractBaseComponent<RenderApp, F>;

Hopefully there is an alternative?

[atlv24]

a blanket impl may be able to do something like this, im not sure exactly what you're trying to do though

[Zeophlite]

Yeah so intention was to prevent the <RenderApp> spam e.g. impl ExtractResource<RenderApp> for Foo {

I think its not too bad as most will just #[derive(ExtractResource)]