[#765] Support MAP over option

Description

Problem: Ithaca introduced another use for MAP instruction, namely it can apply to 'option' types, with the same semantics as Haskell's 'fmap'.

Solution: Add 'TOption' to 'MapOp' and 'Maybe' to 'MapOpHs'. Update typechecker. Add 'instance SingI1 'TOption'

Related issue(s)

Resolves #765 (closed)

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