examples: Add Dynamic Types reflection example

[MrGVSV]

Objective

Dynamic types can be tricky to understand and work with in bevy_reflect. There should be an example that shows what they are and how they're used.

Solution

Add a Dynamic Types reflection example.

I'm planning to go through the reflection examples, adding new ones and updating old ones. And I think this walkthrough style tends to work best. Due to the amount of text and associated explanation, it might fit better in a dedicated reflection chapter of the WIP Bevy Book. However, I think it might be valuable to have some public-facing tutorials for these concepts.

Let me know if there any thoughts or critiques with the example— both in content and this overall structure!

Testing

To test these changes, you can run the example locally:

cargo run --example dynamic_types

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Changelog

• Add Dynamic Types reflection example

[alice-i-cecile]

Really lovely! I was butting my head against this for the dev tools RFC and I'm grateful to have such a clear explanation to refer back to.

I'm perfectly fine with this style of material living in the examples for now. Like you said, I think it's a better fit for the book in the long-term, but we can cross that bridge later :)

[pablo-lua]

Very good explanation on this feature! There is a very good amount of knowledge here that can be of use to beginners, all good.

[cBournhonesque]

Just so I understand; they could if we just provided an API typed_deserialize<T> -> T
(instead of the deserialize -> dyn Reflect that we have?

[MrGVSV]

Yep! I had considered mentioning how we could automatically use ReflectDefault or ReflectFromReflect internally but I figured that was an unnecessary technical note

[cBournhonesque]

Really useful explanation, love this!