General feedback of KHR_interactivity support

Hi folks, as discussed in the Khronos Interactivity TSG meeting I'd like to summarize some feedback from tech artists and software devs about authoring interactivity with UnityGltf. These feedback is from a hackathon in July so it may be a bit outdated, but raising it here in case it's helpful.

# The Good
First of all, thanks everyone for working on this. Many people are familiar with Unity and found the visual scripting easy to integrate with their existing Unity workflow. It's great to have glTF Interactivity support in a fully featured editor.

# Constructive feedback

- Searching for nodes (particularly that glTF support) is a tough process.
- Would have appreciated warnings earlier in the process about how the animations would fail to export! I exported several times and only saw them towards the end.
- Some weird issues that weren’t documented or intuitive. Sometimes iterating over child nodes was not possible, so you would have to attach a graph to each object to animate it as an example.
- Debugging (both during development and export) lacks a lot of detail making the process difficult

# Suggestion
I believe runtime playback for Interactivity like #849 will be very useful for other interactivity runtime developers and interactivity graph authors. This makes iteration faster - we won't need to export and upload the glb to somewhere else for validation. It's not great to manage a dozen versions of the same asset.

### Steps to reproduce 🔢

N/A

### Files to reproduce the issue ♻

_No response_

### Editor Version 🎲

2021.3

### Render Pipeline and version

N/A

### UnityGLTF Version

N/A

### Operating System 👩‍💻

macOS

### When does this problem happen?

- [ ] Editor Import
- [ ] Runtime Import
- [ ] Editor Export
- [ ] Runtime Export

### Additional Info 📜

_No response_

### Validations 🩹

- [x] I have [searched existing issues](https://github.com/KhronosGroup/UnityGLTF/issues): no issue already exist that reports the same problem.
- [x] I follow the [Code of Conduct](https://www.khronos.org/about/code-of-conduct)
- [ ] I provided a [minimal reproducible example](https://stackoverflow.com/help/minimal-reproducible-example), including files when necessary.

Start by reviewing the runtime playback proposal in issue #849 and the existing UnityGLTF interactivity support. The feedback spans node search, export warnings, child-node iteration, debugging, and runtime validation, but names no files or reproducible case. Done would require a scoped decision and implementation target rather than addressing the entire feedback list.

Written by the indexing model from the issue text.