Allow Building of Avatars with Mono on Linux

[SylanTroh]

Is your feature request related to a problem?

Linux uses Mono for its Windows build support, rather than IL2CPP.

So CheckIfIL2CPPIsInstalled() will always be false even if Windows build support is installed on Linux.

Describe your preferred solution

I managed to get avatar builds on Linux working with the following two changes:

1. I changed my scripting backend to Mono in Project Settings > Player (I am unsure if this can be automated, but it would be nice)
2. I changed the CheckIfIL2CPPIsInstalled function to also check for Mono

public static bool CheckIfBuildSupportIsInstalled()
{
    Debug.Log("Checking if IL2CPP or Mono is installed...");

    var playbackEndingDirectory = BuildPipeline.GetPlaybackEngineDirectory(EditorUserBuildSettings.activeBuildTarget, BuildOptions.None, false);
    bool isIL2CPPInstalled = !string.IsNullOrEmpty(playbackEndingDirectory) && Directory.Exists(Path.Combine(playbackEndingDirectory, "Variations", "il2cpp"));
    bool isMonoInstalled = !string.IsNullOrEmpty(playbackEndingDirectory) && Directory.Exists(Path.Combine(playbackEndingDirectory, "Variations", "mono"));

    bool isInstalled = isIL2CPPInstalled || isMonoInstalled;
    
    Debug.Log(isIL2CPPInstalled ? "IL2CPP is installed." : "IL2CPP is NOT installed.");
    Debug.Log(isMonoInstalled ? "Mono is installed." : "Mono is NOT installed.");
    return isInstalled;
}

Describe any considered alternatives

I am unsure what consequences doing the above are for Windows, so I can't comment on that.

In any case, I think I could live with changing the scripting backend manually, since that's a one time change. But the build scripts should definitely be changed to check for build support in general, rather than IL2CPP in particular.

Additional Context

No response

[dooly123]

i am going to make it a fall-through system where if il2cpp is found it uses that else it uses mono. (i can always assume mono exists)

[dooly123]

ok this should solve it, will roll it for testing soon. however, will be a week realistically before its in use. (will be apart of the bundle format change)

[dooly123]

this is now solved on lts, can you please double check that it works for me ty