Incorrect handling of using keyword with async #1571

The using keyword does not work properly when combined with async. Take the following typescript code:

async function getResource(): Promise<AsyncDisposable> {
  return {
    [Symbol.asyncDispose]: async () => {
      console.log("Dispose async!");
    }
  };
}

async function someOtherAsync() {
    // Do async work...
}

async function main() {
  await using resource = await getResource();
  await someOtherAsync();
}

main();

This code compiles and works as expected. However, attempting to compile this with tstl results in the following errors:

Await can only be used inside async functions.(typescript-to-lua)

The error happens at await someOtherAsync(), presumably because the way tstl compiles the using keyword does not account for the function being async in the protected call.