feat: add parley in example

[Hennzau]

Hi, I found that this repository was missing a good text rendering example with parley so I added it in the current simple example.

Please tell me if you prefer a separate example for this :)

[DJMcNab]

Sorry it's taken a while to get to reviewing this - it's something where I'm not sure what the right answer here is. A few thoughts:

1. Unfortunately, the simple example is definitely not the right place for this to live. This is because it is designed to show the simplest possible viable integration between Vello and Winit (whether or not that actually covers all the details is a question we don't answer here). As such, including Parley in this example is definitely not right.
2. Having a way for people to learn that the right way (well, one of them) to handle text layout in Vello is using Parley is important, and an example is a reasonable way to achieve this.
3. Our scenes use something called SimpleText, which is a simple and therefore wrong text layout engine. It would be really good to replace that with Parley instead.

So concretely, I think what should happen in this PR is:

1. The changes to the simple example are reverted.
2. The examples in Vello which use SimpleText should be refactored to use Parley. The easiest option here is to make SimpleText internally use a Parley Layout. That is of course incorrect in general, but we can leave a comment that you should actually be retaining the Layout.

Hope this makes sense.