Fix OnApplicationStart DllNotFoundException in Unity Editor for Windows

[Pomdap]

Issue

When starting the Unity Editor on Windows while using AppleUnityPlugins, we get the following error:

DllNotFoundException: AppleCoreNativeMac assembly:<unknown assembly> type:<unknown type> member:(null)
Apple.Core.Availability.OnApplicationStart () (at ./Packages/com.apple.unityplugin.core/Runtime/Availability.cs:13)

Expected behaviour

We should not get any Error in the Editor.

Fix

Add ifdef around the Dll imported methods.