feat: add experimental features

[aarthificial]

Adds a project setting for enabling experimental features:

// project.ts

export default makeProject({
  experimentalFeatures: true,
  // ...
});

The setting can be accessed in the UI:

const {project} = useApplication();
console.log(project.experimentalFeatures);

As well as in the runtime code:

const scene = useScene();
console.log(scene.experimentalFeatures);

Once enabled, the UI displays the following indication:

[hhenrichsen]

Couple minor questions, no blockers. Excited to be able to use this for fun new APIs!