Add function for checking modules for type piracy, ambiguities, etc in defined rules

Given an example like

struct Foo end

(f::Foo)(x) = x^2

function ChainRulesCore.rrule(::typeof(Foo), x)
    Foo_pullback(Δy) = (NO_FIELDS, x' * Δy + Δy * x')
    return x^2, Foo_pullback
end

Because typeof(Foo) is DataType, this common mistake is highly piratical and will subtilely and completely break AD packages like Zygote for anyone who has this rule in their namespace (it should be ::Foo in the signature, not typeof(Foo)).

On Slack, @oxinabox suggested:

We should think about tools to make this more obvious.
Maybe something that lists the true things that have been targetted by all rules defined in a package?

I suggested:

Something like ChainRulesTestUtils.check_all_rules(MyModule) which as much as possible checks for things like type piracy, ambiguities, etc?

Start by reviewing the proposed ChainRulesTestUtils.check_all_rules(MyModule) entry point and the Julia rule example in this issue. Determine how the utility should identify incorrect targets, type piracy, and ambiguities, then define checks and completion criteria for reporting those problems across a module.