wit-parser: extend WasmImport for future/stream intrinsics

[peter-jerry-ye]

Fixes #2409.

The intention is to hope that in wit-bindgen, we no longer need to concat strings to make up the name ourselves. And this hopefully can make the transition easier from the legacy naming to the standard32 naming.

Summary

• Extend wit_parser::WasmImport with FutureIntrinsic and StreamIntrinsic variants.
• Add FutureIntrinsic / StreamIntrinsic enums in wit-parser.
• Implement Resolve::wasm_import_name support for these intrinsic imports under legacy mangling.
• Keep Standard32 unsupported for future/stream intrinsics with an explicit message (current model is sync-only).
• Refactor wit-component dummy module generation to keep declarative import templates while sourcing intrinsic names from resolve.wasm_import_name(...).

Validation

• cargo clippy -p wit-parser --all-targets -- -D warnings
• cargo clippy -p wit-component --all-targets -- -D warnings
• cargo test -p wit-parser wasm_import_name_future_and_stream_intrinsics
• cargo test -p wit-component

[alexcrichton]

Thanks!