feat(xplat-v9): adding a webapp to test the code, and cleanups

[kelset]

ℹ️ Note: This is being merged into the xplat branch, not master

Description

This PR does a couple of things:

1. it adds a new small web app under the web folder. This mimiks something we've done in the past for other xplat projects (see here) and allows to verify that the code works directly on both the native platforms and web. (see screenshots below)
2. it cleans up the code a bit, removing unused code.

While working on this code, I've hit two different issues:

• on mobile (iOS and Android), the layout is not respected. Despite the StrictDomDemo being wrapped in a View it goes outside its boundaries (you can see it in the screenshot). This needs to get investigated & fixed separately.
• on Android, one of the Buttons, Shape to be precise, crashes the app with the error: Error while updating property 'borderBottomRightRadius' of a view managed by: RCTView java.lang.String cannot be cast to java.lang.Double - this one also needs to be investigated separately, for now I've commented that specific button out.

Screenshot

Here's the code working across iOS-Android-macOS-web:

And here's a quick GIF showing that it's literally the same code:

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