feat(library/hop_match): make the higher order pattern matcher slightly stronger
feat(library/hop_match): make the higher order pattern matcher slightly stronger

It now can handle (?m t) where t is not a locally bound variable, but ?m and all free variables in t are assigned.

Signed-off-by: Leonardo de Moura <7610bae85f2b530654cc716772f1fe653373e892@microsoft.com>

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