Refactor: Engine

[Felix Frank (feliopterix)]

1. Why is this change necessary?

To improve on maintainability and accessibility for developers, we want to expose the vital parts of dive to the public. By doing so, a foreign developer can access dive's core parts and use it like a normal three.js application if needed.

2. What does this change do, exactly?

Exposes the newly created engine in the dive instance. Engine class contains Renderer, Scene, Render Pipeline and Camera.

3. Describe each step to reproduce the issue or behaviour.

import { DIVE } from '@shopware-ag/dive';

const dive = new DIVE();

const scene = dive.engine.scene;
const renderer = dive.engine.renderer;
const camera = dive.engine.camera;

4. Please link to the relevant issues (if any).

Depends on: #65

5. Checklist

• I have rebased my changes to remove merge conflicts
• I have written tests and verified that they fail without my change
• I have written or adjusted the documentation according to my changes
• This change has comments for package types, values, functions, and non-obvious lines of code
• I have read the contribution requirements and fulfil them.