Promote many simple const variables to constexpr

[tcoyvwac]

As encouraged and suggested in Mixxx's Coding Guidelines:

---

constexpr

Use whenever possible, [...]

---

https://github.com/mixxxdj/mixxx/wiki/Coding%20Guidelines#constexpr

[Be-ing]

Thank you for this nice contribution. Please sign the Contributor Agreement and leave a comment here before we can merge this.

I would prefer to ignore pre-commit's reformatting in this special case to minimize the potential for merge conflicts.

[tcoyvwac]

Hello @Be-ing , I would like to sign the Contributor Agreement, but I do not have the ability to use the site. Is there another alternative place where the Agreement can be signed? Or another way to confirm somehow? Thanks for your positive feedback!

[ronso0]

This is the correct link
https://docs.google.com/forms/d/e/1FAIpQLScC9QG327sjLL0eWftmfGUasxFFLxg6LCXJ2xHDYRzFIRqyiw/viewform?formkey=dEpYN2NkVEFnWWQzbkFfM0ZYYUZ5X2c6MQ

[ronso0]

please squash the commits (as long as no in-line review comments have been made).

[tcoyvwac]

Agreement signed and commits squashed.

[Be-ing]

Thank you.

[Be-ing]

Please setup pre-commit before starting another branch. I made an exception in this case because the autoformatting would have made this diff way bigger and increased the chance of merge conflicts across many files.

[tcoyvwac]

Agreed and very much appreciate the (trade-off) exception @Be-ing! 😄 🎉 For changes like these, I agree, a small / the smallest merge footprint was the aim, and strongly preferred.

Grateful for understanding of what the PR (in context) was trying to achieve. 👍