feat: Add WASI Preview 2 support and enhanced target coverage

[avrabe]

Summary

Add wasm32-wasip2 to DEFAULT_EXTRA_TARGET_TRIPLES following the same pattern as wasm32-wasip1. This ensures WASI Preview 2 toolchains are generated out-of-the-box alongside Preview 1, providing consistency for users working with both WASI versions.

Changes

• Target Triple Registration: Add wasm32-wasip2 to DEFAULT_EXTRA_TARGET_TRIPLES in rust/private/repository_utils.bzl

This addresses the feedback from @cameron-martin to include wasm32-wasip2 in the default extra target triples for automatic toolchain generation.

[cameron-martin]

This looks very useful, thanks.

I'm not sure what the policy for this repo regarding how focused changes are but this looks like at least 3 distinct things are included here:

• Adding features section to README.
• Fixing some issues with cross-compilation toolchains (some changes to the allocator library and tracking some extra input files).
• Adding wasip2 support.

[cameron-martin]

Maybe you could add wasm32-wasip2 to DEFAULT_EXTRA_TARGET_TRIPLES, considering wasm32-wasip1 is there already? This way the wasip2 toolchains are generated out-of-the-box.

[avrabe]

Thanks for the feedback @cameron-martin! You're absolutely right about this covering multiple areas - I'm still learning the contribution patterns here so really appreciate the guidance.

For the DEFAULT_EXTRA_TARGET_TRIPLES suggestion, that makes perfect sense for consistency. I'll add that.

Regarding splitting this up - I'm totally open to that if it would be better for the project. I was trying to get all the WASI P2 pieces working together but I realize that might not align with how changes are typically structured here. Would you recommend breaking it into separate PRs? Happy to follow whatever approach works best.

Thanks for taking the time to review - still getting familiar with the codebase so feedback like this is really helpful.