Add async JavaScript API and JSPI support

[syrusakbary]

This PR takes the subset of changes of the sdk improvements that only affect the API:

• add async module creation and JSPI-backed async functions for the JavaScript backend
• improve JavaScript table element polyfills and add API-focused tests

[Copilot]

Pull request overview

This PR ports async API work into main and extends the wasmer Rust API to support asynchronous module compilation and JSPI-backed async host/guest function calls on the JavaScript backend. It also improves the JS table element polyfills (preserving function types) and adds/adjusts tests to cover these behaviors across native and wasm32 targets.

Changes:

• Add Module::new_async plumbed through backend/module internals, using WebAssembly.compile on the JS backend.
• Implement JSPI-backed async function support for the JS backend (async host functions + async call_async behavior).
• Extend the wasm-types polyfill to translate element sections / table initializers and annotate imported table functions with preserved signatures, with new/updated JS-focused tests.

Reviewed changes

Copilot reviewed 20 out of 21 changed files in this pull request and generated 2 comments.

Show a summary per file

File	Description
lib/api/tests/simple_greenthread.rs	Refactors greenthread test harness to work on native and wasm32; adds task cleanup and wasm-bindgen test coverage.
lib/api/tests/module.rs	Adds async module creation test and a JS table initializer type-preservation test.
lib/api/tests/jspi_async.rs	Restricts a native-only async test to non-wasm32.
lib/api/tests/jspi_async_js.rs	Adds wasm32 JSPI coverage for typed async host/guest calls.
lib/api/src/utils/polyfill.rs	Adds element section parsing + init expr support and records table initializers in the polyfill ModuleInfo.
lib/api/src/utils/native/typed_func.rs	Enables async typed calls on the JS backend via a JS-specific async path; updates async-backend error message.
lib/api/src/entities/module/mod.rs	Introduces public Module::new_async API.
lib/api/src/entities/module/inner.rs	Implements backend-aware async module construction, using JS async compilation on wasm32 JS backend.
lib/api/src/entities/function/inner.rs	Enables creating async functions on the JS backend and wires JS async calls through.
lib/api/src/entities/function/env/inner.rs	Simplifies as_store_async retrieval and adds JS async env variants (JS supported, V8 unsupported).
lib/api/src/entities/engine/mod.rs	Extends supports_async to report JS async capability based on JSPI support.
lib/api/src/backend/js/vm/function.rs	Annotates JS functions with encoded param/result types for later recovery.
lib/api/src/backend/js/mod.rs	Adds the jspi module behind experimental-async.
lib/api/src/backend/js/jspi.rs	Implements JSPI detection/wrappers and an active-store TLS registry used during async calls.
lib/api/src/backend/js/entities/table.rs	Reads preserved function types from JS function annotations when extracting table elements.
lib/api/src/backend/js/entities/module.rs	Adds async JS compilation, stores polyfilled ModuleInfo, and annotates imported table initializer functions.
lib/api/src/backend/js/entities/function/typed.rs	Adds JSPI-backed async typed-call plumbing and result conversion helpers.
lib/api/src/backend/js/entities/function/mod.rs	Implements JS async host function creation + JSPI-backed async guest calls.
lib/api/src/backend/js/entities/function/env.rs	Adds JS async function env types/handles and relaxes Send bounds for JS env accessors.
lib/api/Cargo.toml	Adds wasm-bindgen-futures to the JS feature set; adds wasm32 dev-dep on futures.
Cargo.lock	Updates lockfile to include wasm-bindgen-futures.

Suppressed comments (1)

lib/api/tests/module.rs:18

• This test passes a WAT text string to Module::new_async. On configurations where the wat feature isn’t enabled (e.g. --no-default-features --features js-default), Module::new_async won’t convert WAT to Wasm, so this will fail at runtime. Parse the WAT into Wasm bytes in the test (the wat crate is already a dev-dependency) before calling new_async.

    let store = Store::default();
    let module = Module::new_async(&store, "(module (func (export \"run\")))")
        .await
        .map_err(|error| format!("{error:?}"))?;

[marxin]

As Type is annotated with #[repr(u8)], we can use ty as u8 and use the value directly.

[marxin]

Similarly here.

[marxin]

We should reuse the already existing function parse_serialized_init_expr.

[marxin]

The function likely duplicates already existing function wasmer_compiler::translator::sections::parse_element_section.

[syrusakbary]

I'm actually deleting that in further commits as is not really necessary and we can get by having proper externrefs support

[marxin]

As most of the changes are related to async/JSPI, I would like to see @Arshia001 review of the PR.

[Arshia001]

Async- and JSPI-related bits look good to me. Leaving final approval up to @marxin.