Generate Symbol.dispose on classes

[H-Plus-Time]

Implements #4117 (Explicit Resource Management support).

The main things I can think of for additional tests here are:

1. A basic Deno-only test involving using.
2. The polyfill mechanism (not worth it given the simplicity)

[daxpedda]

I didn't fully review this yet, but considering its not standard yet, this should be behind an experimental flag.

Otherwise I'm happy to include this.

[H-Plus-Time]

Gating behind an experimental flag I think would be more trouble than it's worth, for a few reasons:

1. At worst, it is a no-op (Symbol.dispose exists uniquely, or not at all).
2. Integrating tools (wasm-pack, basically) would need to account for said flag.
3. While the overall proposal is at stage 3, Symbol.dispose is on the far side (in the sense that the symbol name and meaning have been settled for several years).

[daxpedda]

1. At worst, it is a no-op (Symbol.dispose exists uniquely, or not at all).

My worry is that if something changes, for whatever reason, we would need a breaking change.

2. Integrating tools (wasm-pack, basically) would need to account for said flag.

Indeed. We could do it via an environment variable, like many other features.

3. While the overall proposal is at stage 3, Symbol.dispose is on the far side (in the sense that the symbol name and meaning have been settled for several years).

Unfortunately I'm not well versed in the JS ecosystem at all, my experience so far has been that things change a lot. From the looks of it I agree that this is very unlikely to change, but I don't want to bet on it.

[H-Plus-Time]

Oh, right, environment variables - yep, I'm fine with that, provided it's discoverable.

[daxpedda]

I explicitly added EXPERIMENTAL to the name and added a changelog entry.

Thank you!