Support editing textScaleFactor, brightness, etc. in devtools

The ability to switch between dark/light mode, adjust text scale, switch target platform (iOS, Android, etc.) would allow devs to quickly verify that their widget functions as expected in a variety of environments.

To illustrate the benefit this would provide, the current flow for switching between dark/light mode on an iOS simulator is:
- Open the Settings app
- Open the Developer page
- Toggle "Dark appearance"

Even worse, changing text scale:
- Open the Settings app
- Open the Accessibility page
- Open the Display & Text Size page
- Open the Larger Text page
- Drag the slider up or down to adjust text scale

Having a way to do this without so many clicks and without having to leave the app would be phenomenal.

https://pub.dev/packages/device_preview demonstrates a version of the functionality that would be great to have as part of DevTools.