Add tests to Rive to act as an example for users, as well as testing the downstream repository

[HayesGordon]

[JulianBissekkou]

A few things that I would include in those tests:

• Simple widget tests where an interaction with rive happens
• Golden test (since devs might exchange rive files in the project that are used across multiple screens)
• Example project with a workspace (it's important that the native binaries are correctly downloaded and installed, this failed previously)
• Build an example project with flavors on all target platforms (also failed previously)