Fix C# string chars getter in AOT build

Source/Engine/Engine/NativeInterop.Unmanaged.cs

@@ -473,13 +473,12 @@ namespace FlaxEngine.Interop
         /// Returns pointer to the string's internal structure, containing the buffer and length of the string.
         /// </summary>
         [UnmanagedCallersOnly]
-        internal static IntPtr GetStringPointer(ManagedHandle stringHandle)
+        internal static char* GetStringPointer(ManagedHandle stringHandle, int* len)
         {
             string str = Unsafe.As<string>(stringHandle.Target);
-            IntPtr ptr = (Unsafe.Read<IntPtr>(Unsafe.AsPointer(ref str)) + sizeof(int) * 2);
-            if (ptr < 0x1024)
-                throw new Exception("null string ptr");
-            return ptr;
+            *len = str.Length;
+            fixed (char* p = str)
+                return p;
         }
 
         [UnmanagedCallersOnly]
@@ -786,7 +785,7 @@ namespace FlaxEngine.Interop
             }
 
             string assemblyPath = Marshal.PtrToStringAnsi(assemblyPathPtr);
-            
+
             Assembly assembly;
 #if FLAX_EDITOR
             // Load assembly from loaded bytes to prevent file locking in Editor

Source/Engine/Scripting/Runtime/DotNet.cpp

@@ -245,12 +245,6 @@ struct NativePropertyDefinitions
     MMethodAttributes setterAttributes;
 };
 
-struct NativeString
-{
-    int32 length;
-    Char chars[1];
-};
-
 MDomain* MCore::CreateDomain(const StringAnsi& domainName)
 {
     return nullptr;
@@ -369,9 +363,10 @@ MString* MCore::String::New(const Char* str, int32 length, MDomain* domain)
 
 StringView MCore::String::GetChars(MString* obj)
 {
+    int32 length = 0;
     static void* GetStringPointerPtr = GetStaticMethodPointer(TEXT("GetStringPointer"));
-    NativeString* str = (NativeString*)CallStaticMethod<void*, void*>(GetStringPointerPtr, obj);
-    return StringView(str->chars, str->length);
+    const Char* chars = CallStaticMethod<const Char*, void*, int*>(GetStringPointerPtr, obj, &length);
+    return StringView(chars, length);
 }
 
 MArray* MCore::Array::New(const MClass* elementKlass, int32 length)