[MP] Path simplification does not take visibility into account

### Tested versions

4.3 dev 2

### System information

Windows 10 Godot 4.3 dev 2 Vulkan

### Issue description

Currently, when you would join into a game as a client with host having some nodes considered to be invisible for the client - you are going to get path simplification trying to access missing node.

### Steps to reproduce

1. Start server as host
2. Create a node that inherits from `MultiplayerSynchronizer`
3. Spawn said node with `MultiplayerSpawner`
4. Set its public visibility to `false`
5. Try joining as a client
6. Since this node is *not* going to be spawned by `MultiplayerSpawner` due to visibility influenced by `MultiplayerSynchronizer`, network cache would still try to send node path simplification for a node that does not exist on client, resulting in errors:

### Minimal reproduction project (MRP)

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