Add Dark Mode Support to Firebase Editor App

[mahendra-918]

Feature Request

Implement dark mode support in the Firebase Editor app to enhance user experience, especially for developers working in low-light environments.

Proposed Solution:

Use Flutter's ThemeData to define both light and dark themes.
Add a toggle switch in the app settings to allow users to switch between light and dark modes.
Persist the user's theme preference using shared_preferences.
Benefits:

Improves accessibility and reduces eye strain for users.
Aligns with modern UI/UX standards that include dark mode support.

[mahendra-918]

hii @chiragtyagi2003 sir can you please assign me this