Provide a Pkl renderer

[bioball]

There should be a renderer that renders Pkl output.

Use-cases:

• Eschew the need to create converter modules like https://pkl-lang.org/package-docs/pkg.pkl-lang.org/pkl-pantry/k8s.contrib/current/convert/index.html
• Ability to programmatically rewrite Pkl using Pkl itself

Imagined usage:

output {
  renderer = new PklRenderer {}
  value = someValue
}

Rendered module should be importable in Pkl, and be logically equivalent to someValue.

Output would not retain programming constructs like for/when/amends chains.