[#692] Fix toExpression in combs with var anns

Description

Problem: We try to convert right combs to lists in toExpression, however this transformation is not always lossless. Particularly, if a pair in the comb has annotations, it can't be represented in the list. We check for field and type annotations, but not var annotations.

Solution: Check for var annotations, too.

Also clean up the code a little bit while at it.

Related issue(s)

Resolves #692 (closed)

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