Headless testing and snapshot generation

## Specific Demand

Internally we use [globals, manual events and generations](https://github.com/DioxusLabs/dioxus/blob/9ae3d14e676c90c73a99f5cfb41ff85c7cbf4bc2/packages/core/tests/lifecycle.rs#L44-L78) to test dioxus components. There should be a library that handles some of that setup for you and has a nicer API.

## Implement Suggestion

Features
- Snapshot generation for components, and apps
- Running in a headless browser or without a renderer

Resources:
- https://github.com/microsoft/playwright
- https://dioxuslabs.com/learn/0.4/cookbook/testing#component-testing