set SDLMIXER_VENDORED to ON and vendor the required libraries into libs/SDL3_mixer/external

disable SDLMIXER_VORBIS_VORBISFILE
add ogg v1.3.5-SDL
add opus v1.4.x-SDL
add opusfile v0.13-git-SDL

libs/SDL3_mixer/external/opus/opus_headers.mk

@@ -0,0 +1,9 @@
+OPUS_HEAD = \
+include/opus.h \
+include/opus_multistream.h \
+include/opus_projection.h \
+src/opus_private.h \
+src/analysis.h \
+src/mapping_matrix.h \
+src/mlp.h \
+src/tansig_table.h