Investigate special annotations for LEFT and RIGHT

Clarification and motivation

According to http://tezos.gitlab.io/whitedoc/michelson.html#special-annotations, there are special annotations that can be used on instructions LEFT, RIGHT and PAIR. In 1b98d385 we added special handling for PAIR, but for some reason it's not present for LEFT and RIGHT. Maybe it works correctly already, but we should check that, it's not clear to me.

Acceptance criteria

1. There is a test showing that LEFT and RIGHT instructions with special annotations are handled correctly.
2. If it doesn't pass with current version of our code, the corresponding bug in our code is fixed.