[Math] integral symbol with short horizontal bar in the middle (⨍,⨎)

Dear Wikimedia Community User Group Math,

- We implemented a request from 2016 for the addition of an integral symbol with a short horizontal bar in the middle (⨍,⨎).

- We took the symbols \intbar and \intBar from the stix package as command names.

- The rendering can be reviewed at https://de.wikipedia.beta.wmflabs.org/w/index.php?title=Intbar

- Feedback is possible at https://phabricator.wikimedia.org/T137787

Thanks to everyone who contributed, especially @Stegmujo @Andreg-p @Jdforrester @Mathmensch @pkra, @Christian1985, and Davide P. Cervone from MathJax.

All the best physikerwelt