Fix handling of collections.Counter types

[jrmccluskey]

collections.Counter types are special dictionary cases where they generally only accept one type parameter to act as the key, while the value is implicitly always an int. Beam incorrectly handled these types when properly hinted with only one type, as they are dictionaries but were only being defined with arity 1 instead of 2. This adds a check to correct this issue and an associated test case.

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[jrmccluskey]

assign to next reviewer

[jrmccluskey]

R: @shunping

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