[Build/DevOps] Build & Distribute customised raylib builds with Raylib-cs

[9ParsonsB]

Issue description

Some features of raylib are not enabled in the default/official build for. e.g.

• [Core] Support multiple windows #115
• Android / Xamarin Platform Support #87

Some of these features would be nice to have.

Currently, users have to build raylib themselves if they want these extra features, which causes confusion when many of our users are not familiar with C and/or build systems

Environment

Upstream currently use GitHub Actions, we can probably copy that for the most part.