shells/xonsh: Update to 0.15.1

• Switch to DISTVERSION
• Use pep517 build
• Update comment and pkg-descr
• Take maintainership for the time being

ChangeLog: https://github.com/xonsh/xonsh/blob/main/CHANGELOG.rst
PR: 265044
Reported by: Yonas Yanfa <yonas.yanfa@gmail.com>