multimedia/mpv: update to 0.23.0

• Since ENCA is gone enable UCHARDET by default
• Reduce maintenance by using the same waf version as bootstrap.py

Changes: https://github.com/mpv-player/mpv/releases/tag/v0.23.0
Approved by: cpm (maintainer)
Differential Revision: https://reviews.freebsd.org/D8912