Implement reverse for the remaining operators

[Lythenas]

As a user I want to be able to generate source changes that track through all operators (where possible).

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These operators currently don't implement reverse and therefore can't generate source changes:

• mod
• bit and
• bit or
• bit xor
• shift left
• shift right
• length
• equals
• unequals
• comparison operators
• concat

Note: For some it is not possible to implement the reverse function (or only in very few edge cases).