Steps to reproduce:
1. Open the attached project "VSStrippingCustomUnit.zip"
2. Build and Run
3. Observe that the screen is Red. Checking the Player log you will see a deserialization error. We are still in Scene 1
3. Open Scripts/NodeTest.cs
4. Uncomment line 6 - "// [Preserve]"
5. Build and Run
6. Observe that the screen is Green. Scene 2 was successfully loaded

Expected: Custom Units that are used in Graphs are not stripped under any circumstances
Actual: When using IL2CPP and Medium/High stripping with a custom Unit, the custom Unit is stripped from the build

Reproducible on: Visual Scripting 1.7.8 - 1.8.0 (2021.3.15f1, 2022.1.24f1, 2022.2.0f1, 2023.1.0a20)
Unable to test on 2020.3.41f1 due to Visual scripting errors when downgrading

Notes:
-When using IL2CPP and Medium/High stripping, the custom Unit (NodeTest.cs) is stripped from the build, unless you add the Preserve attribute to the type
-The attached project has two scenes (Scene1 and Scene2). Scene1 has an embedded script graph in it that loads Scene 2 using a custom Unit. Scene1 has a Camera with a red background, Scene2 has a Camera with a green background. The project is set to use IL2CPP scripting backend and has Managed Stripping Level set to High
-Issue only reproduces with IL2CPP scripting backend