WIP: Introduce coerce_any_ref_to_any

[Ralith]

This PR introduces a lint which detects when &Box<dyn Any> is coerced to &dyn Any, which is usually a mistake where the intent was to directly pass the dyn Any inside the box without coercion.

cc @llogiq

Remaining work:

• Documentation
• Generalize from Box to any implementer of Deref<Target=dyn Any>

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[matthiasbeyer]

r? llogiq

[llogiq]

This looks good for a start. Let's add the documentation and replace the "default lint description", and then I can start the Final Comment Period for this lint.