Add Flutter Widget previewer

[MateusHBR]

Describe the feature

Hello!

I suggest implementing the "Widget Previewer" function in Flutter to preview components

This will significantly speed up the development process and increase developer productivity, attracting the Flutter community to use Zed

more info about it https://docs.flutter.dev/tools/widget-previewer

VSCode is a web browser integrated directly into the code editor that compiles Flutter widgets.

If applicable, add mockups / screenshots to help present your vision of the feature