feat(react-shadcn): add new renderer, react-shadcn

[dclark27]

Hi all! I have been working the last week on matching parity with vanilla-renderers (and some features from mui-renderers) that are shadcn compatible.

We've used jsonforms since 2024 at Socotra, and have been rendering using a superset of the vanilla-renderers to achieve shadcn styles since then. To reduce complexity on our end, and to help the broader community, I've taken it on myself to bring these changes we've used in production for several years now to you all.

Obviously we'll need to take time to review this, but I've tested using the examples repo and hit as many cases as I could squeeze in this first iteration. I am deeply familiar with the framework and was able to use Claude Code to take the approach I've been meaning to write on my own since taking on our internal form library.

We'll also need documentation updates, more tests, and perhaps a few changes to this existing implementation.

Putting this up as I have it now to gather feedback and hopefully find a path to merging!

Some screens:

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[dclark27]

I'll fix up the build issues once I get some feedback