x11-wm/mutter: Update to 47.9

Update mutter to version 47.9.

We don't need LIB_DEPENDS on libfontconfig.so, libjson-glib-1.0.so, or
libupower-glib.so. (truckman)

LIB_DEPENDS on libgbm.so is redundant with USE_GL=gbm. (truckman)

Pet porlint. (truckman)

PR: 287932
MFH: 2025Q3