feat: WebGL support for C# layer

samples/unity-of-bugs/Assets/Scripts/MobileNativeSupport/JavaScriptPlugin.jslib

@@ -0,0 +1,9 @@
+mergeInto(LibraryManager.library, {
+
+  ThrowJavaScript: function () {
+    var something = undefined;
+    console.log("JavaScript error incoming...");
+    something.do();
+  },
+
+});

samples/unity-of-bugs/Assets/Scripts/MobileNativeSupport/NativeSupportButtons.cs

@@ -1,6 +1,6 @@
 using System.Collections;
 using System.Collections.Generic;
-#if ENABLE_IL2CPP || PLATFORM_IOS
+#if ENABLE_IL2CPP || PLATFORM_IOS || PLATFORM_WEBGL
 using System.Runtime.InteropServices;
 #endif
 using UnityEngine;
@@ -30,8 +30,13 @@ public void ThrowKotlin()
         {
             jo.CallStatic("throw");
         }
+#else
+// TODO: Add this sample to its own button:
+#if PLATFORM_WEBGL
+        ThrowJavaScript();
 #else
         Debug.LogWarning("Not running on Android.");
+#endif
 #endif
     }
 
@@ -124,6 +129,21 @@ public void ThrowObjectiveC()
     private static extern void throwObjectiveC();
 #endif
 
+    public void ThrowJavaScript()
+    {
+#if PLATFORM_WEBGL
+        throwJavaScript();
+#else
+        Debug.Log("JavaScript interop only works on WebGL players.");
+#endif
+    }
+
+#if PLATFORM_WEBGL
+    // JavaScriptPlugin.jslib
+    [DllImport("__Internal")]
+    private static extern void throwJavaScript();
+#endif
+
     public void LoadBugfarm() => SceneManager.LoadScene("1_Bugfarm");
     public void LoadAdditionalSamples() => SceneManager.LoadScene("3_AdditionalSamples");
 }