docs(example): Example how to insert reflected Component onto entities

[favilo]

Objective

We needed an example that showed how to insert a Component onto an entity that was deserialized into a type that implements Reflect.

ReflectCommandExt::insert_reflect was not easy to discover.

Solution

This new example shows how to use insert_reflect(), while also showing how to deserialize data from glTF extras, and add the deserialized Components automatically to the corresponding scene's children entities on instantiation.

Testing

• Did you test these changes? If so, how?

Tested locally on a Linux machine. Runs fine.

• Are there any parts that need more testing?

It's an example using standard features, so I assume it'll work where ever

• How can other people (reviewers) test your changes? Is there anything specific they need to know?

$ cargo run --example load_gltf_components

• If relevant, what platforms did you test these changes on, and are there any important ones you can't test?

Linux desktop machine. I could potentially test on other platforms like wasm, but I haven't yet.

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[ChristopherBiscardi]

IMO this example should be greatly reduced to essentially only the deserialize_extra that is written and it should be moved to the reflection folder with the more minimal result. gltf extras handling is already shown in the gltf extras example.

Something closer to this would make sense, without any gltf code.

let json_component = r#"{"skein::tests::SomeThings":{"OneThing":{"name":"testing"}}}"#
let type_registry = type_registry.read();

let reflect_deserializer = ReflectDeserializer::new(&type_registry);
let mut deserializer = serde_json::Deserializer::from_str(value);
let reflect_value = reflect_deserializer
    .deserialize(json_component)
    .unwrap();

commands
    .entity(entity)
    .insert_reflect(reflect_value);

Also ron is used in the other examples, I'm not sure if the Bevy repo has a preference for ron over serde_json for the examples

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The generated examples/README.md is out of sync with the example metadata in Cargo.toml or the example readme template. Please run cargo run -p build-templated-pages -- update examples to update it, and commit the file change.

[favilo]

@ChristopherBiscardi, what do you think about this example. I've got both json and ron deserializing, and verify that the component is constructed properly.

[ChristopherBiscardi]

overall lgtm.

A lot of the example is the same as examples/reflection/reflection.rs but I think showing two different serializations (ron/json) is enough to validate the additional example even though insert_reflect could be added to the other example.

I also dislike Foo/Bar naming but the other example this is extended from also uses Foo/Bar so matching that is probably better for ease of recognizing commonalities. CI is failing on the variable foo though so that will have to change to merge.

Notably insert_reflect is hard to find in the documentation because it is on an extension trait, so having an example for it is a good thing.