Update Bepin GOs to use HideAndDontSave flags

[Kein]

Description

To prevent forceful destruction of the manager GOs by the game (see Oddworld: Soulstorm) via
Resources.UnloadUnusedAssets we can use https://docs.unity3d.com/ScriptReference/HideFlags.HideAndDontSave.html

Motivation and Context

Oddworld: Soulstorm (for example) uses aggressive resource management approach that forcefully unloads any objects, including those that were set to DontDestroyOnLoad(). There are 3 possible workarounds:

1. Move away from GameObjects (unlikely, breaking)
2. Use custom loaders for specific game that will patch game's code (unlikely, not relevant to Bepin itself)
3. Resort to easier solution via custom object flags that will prevent it from being unloaded.

How Has This Been Tested?

Preliminary testing on Oddworld: Soulstorm (custom build of Unity 2019.4.12) for about an hour. Plugins used to be destroyed and unloaded after first scene change, now they persist.

Screenshots (if appropriate):

Checklist:

• My code follows the code style of this project.

[ghorsington]

Looks good to me!