Improve flags used for min build size

Suggestions taken from here: https://discussions.unity.com/t/webgl-builds-for-mobile/711925/130
For the ones that are easily exposed in the player settings, and are never changed for the different build targets, I didn't explicitly set them again in code.

Author: JohannesDeml

Assets/Scripts/Editor/BuildScript.cs

@@ -129,9 +129,19 @@ public static void Build(string[] args)
 							buildPlayerOptions.options |= BuildOptions.CompressWithLz4HC;
 							PlayerSettings.WebGL.exceptionSupport = WebGLExceptionSupport.None;
 							SetWebGlOptimization(CodeOptimizationSize);
+							// Off by default, but just to be sure, see https://docs.unity3d.com/Manual/webgl-embeddedresources.html
+							PlayerSettings.WebGL.useEmbeddedResources = false;
+							PlayerSettings.WebGL.threadsSupport = false;
+							// ASTC has the smallest texture sizes
+							EditorUserBuildSettings.webGLBuildSubtarget = WebGLTextureSubtarget.ASTC;
+
 #if UNITY_2022_1_OR_NEWER
 							PlayerSettings.SetIl2CppCodeGeneration(namedBuildTarget, Il2CppCodeGeneration.OptimizeSize);
 #endif
+#if UNITY_6000_0_OR_NEWER
+							// Reduces build size and is widely supported
+							PlayerSettings.WebGL.wasm2023 = true;
+#endif
 #if UNITY_2021_2_OR_NEWER
 							PlayerSettings.SetIl2CppCompilerConfiguration(namedBuildTarget, Il2CppCompilerConfiguration.Master);
 #else