player: add option not to use OSD/fontconfig

Makeshift-solution for working around certain fontconfig issues.

With --use-text-osd=no, libass and fontconfig won't be initialized, and
fontconfig won't block everything with scanning for fonts.
ao_alsa: cleanups

No functional changes.

ALSA_PCM_NEW_HW_PARAMS_API was a pre-ALSA 1.0.0 thing and does nothing
with modern ALSA. It stopped being necessary about 10 years ago.

3 functions are moved to avoid forward references.
audio: make mp_audio_config_to_str return a stack-allocated string

Simpler overall.