Implement WASI.getImportObject and WASI.initialize in node:wasi (#12755, #28534)

[itisrohit]

What does this PR do?

This PR implements two missing Node.js compatibility methods in the `node:wasi` module: `initialize()` and `getImportObject()`. This resolves long-standing compatibility issues for WASI Reactor modules and standardizes the instantiation workflow.

Beyond just adding the methods, this PR addresses a critical instance-safety bug in the original implementation:

• The Bug: The `node:wasi` script was using shared module-level variables (`let fs, bindings`) for its internal operations. Creating multiple `WASI` instances (e.g., for different sandboxed tasks) would result in state pollution across all instances.
• The Fix: Refactored the `WASI` class to use instance properties (`this.bindings`) and ensured all internal WASI import closures capture the correct instance state at construction time.

Key Changes:

• Implemented `WASI.prototype.initialize(instance)`: Correctly handles WASI Reactor modules, validates exports, and sets up memory.
• Implemented `WASI.prototype.getImportObject()`: Provides the standard import object mapping (`{ [version]: this.wasiImport }`) for `WebAssembly.instantiate()`.
• Added strict spec guards: `start()` now throws if `_initialize` is present (Command vs. Reactor check), and vice-versa for `initialize()`.
• Fixed a pre-existing typo (`Recceived` -> `Received`) and several TypeScript lint errors in `wasi.ts`.

How did you verify your code works?

Verification was performed using `bun bd test` with a new comprehensive regression suite and existing WASI tests:

1. Regression Suite (`test/regression/issue/12755.test.ts`):
   • Verified existence and type of `initialize` and `getImportObject`.
   • Tested dynamic versioning in `getImportObject` (supporting both `preview1` and `unstable`).
   • Instance Isolation Test: Verified that two `WASI` instances with different filesystem bindings do not conflict with each other.
   • Tested strict spec guards for `_start`/`_initialize` overlapping.
2. Existing Tests:
   • Verified that `test/js/bun/wasm/wasi.test.js` still passes.
3. Linter & Code Quality:
   • Confirmed `oxlint` passes with 0 warnings/errors.
   • Confirmed `prettier` formatting is consistent with project style.

Tested on macOS with `bun bd`.

[claude]

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