Fix saving hyperparameters in a composition where parent is not a LM or LDM

[awaelchli]

What does this PR do?

Fixes #13181
Closes: #13202

Look at this code:

    class Child(LightningModule):
        def __init__(self, same_arg):
            super().__init__()
            self.save_hyperparameters()

    class Parent: 
        def __init__(self, same_arg="parent_default", other_arg="other"):
            self.child = Child(same_arg="cocofruit")

    parent = Parent()
    print(parent.child.hparams)

Note: There is a LightningModule composed inside of a non-LightningModule class.

Q: At the call self.save_hyperparameters(), which parameters do we excpect to get saved?
A: Only the ones from the child LightningModule. But on master, it collects also the ones from the parent class.

Q: But Adrian, collecting more parameters is always better. The more the better!
A: No. 1) You could coincidentally have two arguments with the same name in two different classes. So there is a collision and in master, one overwrites the other. Bad! 2) We save hyperparameters not just for the sake of saving them. We want to save exactly the ones needed to reconstruct the object when loading ChildInComposition.load_from_checkpoint. No more, no less.

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cc @Borda @justusschock @awaelchli @ninginthecloud @rohitgr7 @otaj @akihironitta