Add compat flag docs for FinalizationRegistry and WeakRef

[ketanhwr]

Summary

Add docs for WeakRef compat flag.

Screenshots (optional)

Documentation checklist

• The documentation style guide has been adhered to.

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PR Change Summary

Added documentation for the compatibility flags related to FinalizationRegistry and WeakRef.

• Introduced documentation for the enable_weak_ref and disable_weak_ref flags.
• Provided explanations for FinalizationRegistry and WeakRef functionalities.
• Included notes on the behavior and caution regarding the non-deterministic nature of these APIs.

Added Files

• src/content/compatibility-flags/js-weak-refs.md

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[irvinebroque]

Do we have an example, and an example use case that we could share as part of this?

Def changelog worthy, esp if we help people connect the dots to what this makes possible w/WASM @mikenomitch

[ketanhwr]

We can definitely mention that wasm-bindgen and Emscripten optionally use FinalizationRegistry for wasm memory cleanup, but it's part of the generated shim and a user would hardly need to interact with it directly. Not sure if adding an example is helpful here really

[irvinebroque]

It improves memory management for workers-rs, right? That seems like a story right there?

[ketanhwr]

Will definitely improve memory management for all wasm users frankly, not just workers-rs :)

[irvinebroque]

Awesome - let's tell the story and explain! @mikenomitch

[irvinebroque]

Are we going to write a changelog entry for this?

https://developers.cloudflare.com/changelog/

And show examples? Or explain what this means for workers-rs?

[ketanhwr]

Are we going to write a changelog entry for this?

https://developers.cloudflare.com/changelog/

And show examples? Or explain what this means for workers-rs?

@danlapid @mikenomitch what do you think? We can certainly mention this in workers-rs or "Rust" section of workers docs. We can possibly have a changelog mentioning improvement in wasm interop/memory usage, but I don't think we want to explicitly advertise the FinalizationRegistry API.

[ketanhwr]

@irvinebroque @mikenomitch let me know if this looks good, the compat date is due soon so I'd want this to be available in docs before that

[mikenomitch]

Approved to unblock, but added a suggested change to changelog