We need to be building the Unity tests on CI for all platforms and all scripting backends. Since Unity cannot cross-compile with IL2CPP, we'll need to build on Linux, macOS, and Windows separately.

Rough breakdown of the tasks is:

• [x] _{Prepare a cross-platform Github action for building the Unity test runner}
  • [x] Needs to run editor in -batchmode
  • [x] Needs to obtain a floating license and release it once done
• [x] Provision self-hosted Linux instance for building for Linux and Android.
  • [x] Needs the Unity editor installed
  • [x] Needs workloads for Linux (Mono and IL2CPP) and Android
  • [x] Needs to be able to connect to the licensing server
• [ ] @bwachter Provision self-hosted macOS instance for building for macOS and iOS
  • [ ] Needs the Unity editor installed
  • [ ] Needs workloads for macOS (Mono and IL2CPP) and iOS
  • [ ] Needs to be able to connect to the licensing server
• [ ] Provision self-hosted Windows instance for building for Windows and UWP
  • [x] Needs the Unity editor installed
  • [x] Needs workloads for Windows
  • [x] Needs to be able to connect to the licensing server
  • [x] (@bwachter) Update unity-editor script to retry the build if we hit a license limit
  • [x] (@bwachter) Update unity-editor to log output from the returnlicense call
  • [ ] (@nirinchev) Test IL2CPP scripting backend
  • [x] (@bwachter) Install win10 sdk: Windows 10 SDK is not installed. You can install from here: https://developer.microsoft.com/en-us/windows/downloads/windows-10-sdk/.
  • [x] (@bwachter) unity-editor should return an error code if the build fails.