Fix exception propagation when preparing await

[xeioex]

Fixes #1757.

Errors while preparing await currently reject the async function's outer promise directly, skipping its catch and finally blocks. Resume the function with the pending exception instead, including errors from callback creation and promise reaction allocation.

The specification requires Await to propagate an abrupt completion from PromiseResolve, including a throwing promise.constructor getter:

• Await: https://tc39.es/ecma262/multipage/control-abstraction-objects.html#await
• PromiseResolve: https://tc39.es/ecma262/multipage/control-abstraction-objects.html#sec-promise-resolve

For example:

const p = Promise.resolve(1);
Object.defineProperty(p, "constructor", {
    get() { throw new Error("boom"); }
});

(async () => {
    try {
        await p;
    } catch (e) {
        console.log(e.message);
    } finally {
        console.log("cleanup");
    }
})();

Expected output: boom, then cleanup. Both blocks are skipped before the fix.

A finally block can also override the exception:

(async () => {
    try {
        await p;
    } finally {
        return 42;
    }
})().then(console.log); // 42

Validation:

• Regression test passes in QuickJS and Node.js 25.2.1.
• Fault injection confirms catch/finally run after allocation failures.
• Project tests and focused async test262 pass under clang-18 ASan/UBSan.
• Full Release test262: 82,220 checks, no new failures against the baseline.