Add TeXstudio support

Summary:
Some people need it because it is now the default TeX editor in distributions.

BUG: 404120

Test Plan: "Settings -> Configure Okular... -> Editor -> TeXstudio". Should work for the reverse search if the tex file is compiled with \usepackage[active]{srcltx}

Reviewers: #okular, ngraham

Reviewed By: ngraham

Subscribers: ngraham, okular-devel, kde-doc-english

Tags: #okular, #documentation

Differential Revision: https://phabricator.kde.org/D19272