contrib: vpx: update to 1.12.0

Notable changes:
 - This release adds optimizations for Loongarch, adds support for vp8 in the
   real-time rate control library, upgrades GoogleTest to v1.11.0, updates
   libwebm to libwebm-1.0.0.28-20-g206d268, and includes numerous bug fixes.

Bug fixes:
 - Fix to a crash related to {vp8/vp9}_set_roi_map.
 - Fix to compiling failure with -Wformat-nonliteral.
 - Fix to integer overflow with vp9 with high resolution content.
 - Fix to AddNoiseTest failure with ARMv7.
 - Fix to libvpx Null-dereference READ in vp8.