Fix bubleCleanup es6 class unwrapping

[ianpurvis]

I found that buble does not always place the prototype and constructor assignment at the end of the es6 class wrapper, which was breaking the transform for AudioListener (#19934 (comment))

This makes the string replacement more agnostic about where things are located. I also added some captures for some extra safety around the es6 class and parent class names.

Supports #11552

[mrdoob]

Thanks for working on this 🙏

I've studied the problem and this is what's happening.

So far bubleCleanup was only able to handle buble's output of this:

class Dog extends Animal {

    constructor() {}

}

This PR adds support for buble's output of this:

class Dog extends Animal {

    constructor() {}

    bark() {}

    ...

}

[mrdoob]

Thanks!