fix: add isClassPrivateMethod() to esm-transformer

[nytamin]

Bug fix

This PR adds the check isClassPrivateMethod() to the detectESMFeatures topLevelAwait checks, to exclude private-hashtag-methods from bein considered top-level.

Background

I found a bug where I got the message path/to/file.js has both top-level await and export statements..., even though I had reduced the file in question to be simply:

export class MyClass {
  async #myMethod() {
    await Promise.resolve()
  }
}

Adding parent.isClassPrivateMethod() to the checks fixed the issue for me locally.