Refactor cloud layer [2021.2]

[adrien-de-tocqueville]

Purpose of this PR

This PR change the cloud layer interface to add more settings, mainly option to have two layers of clouds, it also adds a basic lighting option and an option to have clouds cast shadows for the sun light.

The PR also add the possibility for volume components to have nested parameters
For example:

public class Component: VolumeComponent
{
    // This doesn't change
    public ClampedFloatParameter a = new ClampedFloatParameter(0.0f, 0.0f, 1.0f);

    // This is now possible
    [Serializable]
    public class NestedClass
    {
        public ClampedFloatParameter b = new ClampedFloatParameter (0.0f, 0.0f, 1.0f);
    }

    public NestedClass nested = new NestedClass();
}

The PR is not ready yet because the default cloud map needs to be redone
Errors on Vulkan:

• on yamato "Compute dispatch: missing constant buffer"
  after check, this error also happens on staging but the test still work (it might need to be fixed though)
• sometimes on local machine "Compute dispatch: missing texture ID"
  probably related to the shadow texture, but it is quite random

---

Testing status

• Tested with all skies
• Tested disabling sunlight
• Putting a cubemap in the cloud map slot writes an error to the console (this happens on other components also, don't know if this is the right thing to do)
• Tested texture baking
• Tested with/without static sky

Updated test scene 5010 to include new features

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Comments to reviewers

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