Feature/add mathml definitions

[fekete965]

This PR is trying to address the following issue: #4208
The MathML interfaces were based on the MDN documentation: https://developer.mozilla.org/en-US/docs/Web/MathML
The high commit count could look intimidating, but each commit contains a small change by introducing a new MathML tag.

[coveralls]

coverage: 99.463%. remained the same
when pulling 6eb5309 on fekete965:feature/add-mathml-definitions
into f3d4271 on preactjs:main.

[fekete965]

I will double-check each element and the corresponding definition this week.

[fekete965]

I think the PR is good for a review 🙈

[marvinhagemeister]

Sweet, thank you so much for adding this 👍