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_sources.mk

@@ -0,0 +1,16 @@
+OPUS_SOURCES = \
+src/opus.c \
+src/opus_decoder.c \
+src/opus_encoder.c \
+src/opus_multistream.c \
+src/opus_multistream_encoder.c \
+src/opus_multistream_decoder.c \
+src/repacketizer.c \
+src/opus_projection_encoder.c \
+src/opus_projection_decoder.c \
+src/mapping_matrix.c
+
+OPUS_SOURCES_FLOAT = \
+src/analysis.c \
+src/mlp.c \
+src/mlp_data.c