Hacked buffer memory alignment for the iOS/tvOS simulator

When running in the iOS/tvOS simulator, constant buffer offsets must be
aligned to 256 bytes. `vkGetBufferMemoryRequirements` is reporting the
wrong alignement in this case. see: KhronosGroup/MoltenVK#1250

src/vk_mem_alloc.h

@@ -15196,6 +15196,10 @@ void VmaAllocator_T::GetBufferMemoryRequirements(
         requiresDedicatedAllocation = false;
         prefersDedicatedAllocation  = false;
     }
+#if TARGET_OS_SIMULATOR
+    // See: https://github.com/KhronosGroup/MoltenVK/issues/1250
+    memReq.alignment = 256;
+#endif
 }
 
 void VmaAllocator_T::GetImageMemoryRequirements(