Add NoProductType and NoSumType constraints

[kleinreact]

The PR adds constraints to BitPack, which allow to check the instance type for being no sum- or no product type. Checking negated properties results from the limitation that constraints can only be composed conjunctively in this case, which is required for recursive detection over the generic structure.

An alternative Bool-based implementation is provided by #3030.

Still TODO:

• Write a changelog entry (see changelog/README.md)
• Check copyright notices are up to date in edited files

[martijnbastiaan]

This won't be necessary anymore because #3029 (comment).