Add wideint exponentation instructions WDEX and WQEX

[Dentosal]

(requested in a slack discussion)

PR is still WIP, missing tests. Also needs spec PR.

Checklist

• Breaking changes are clearly marked as such in the PR description and changelog
• New behavior is reflected in tests
• If performance characteristic of an instruction change, update gas costs as well or make a follow-up PR for that
• The specification matches the implemented behavior (link update PR if changes are needed)

Before requesting review

• I have reviewed the code myself
• I have created follow-up issues caused by this PR and linked them here