Improving RN Skia Docs (WIP 🏗️)

[kimchouard]

⚠️ WORK IN PROGRESS ⚠️ This is PR still under development, do not merge it yet. :)

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This is a global PR aiming at improving RN Skia's docs.

Improvement List

• [x] Better Metro bundler support & onboarding
• [ ] Better visibility on Paths possibilities (providing alternatives in the shape pages, e.g. path.addRect(...) instead of <Rect />)
• [ ] Improve the painting section (more examples, incl. Skia.(...), and provide link to those from the shape pages
• [ ] Better documentation on asset loading for Web (require returns a number in Metro, which makes the script fail, e.g. when loading fonts)
• [ ] Live examples with dynamic snacks 🍿 🛠️ PENDING on fix a for #2108
• [ ] Adding canvasKitJs documentation when merged

Feel free to share more ideas here on what could/should be done to improve the docs.