Simplify the implementation of `binOpOffset` if possible

[jberthold]

PR #746 implements binOpOffset by extending the Metadata for pointers and references.
An outline of an alternative, and possibly simpler, implementation is written in branch 709-binOpOffset-again.

• Attempt to refactor the existing implementation as described in the notes.
• Maybe combine this with Add exec-smir tests for offset #764 - adding more tests for binOpOffset.