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/doc/Makefile.am

@@ -0,0 +1,45 @@
+## Process this file with automake to produce Makefile.in
+
+DOCINPUTS = $(top_srcdir)/include/opus.h \
+            $(top_srcdir)/include/opus_multistream.h \
+            $(top_srcdir)/include/opus_defines.h \
+            $(top_srcdir)/include/opus_types.h \
+            $(top_srcdir)/include/opus_custom.h \
+            $(top_srcdir)/doc/header.html \
+            $(top_srcdir)/doc/footer.html \
+            $(top_srcdir)/doc/customdoxygen.css
+
+EXTRA_DIST = customdoxygen.css Doxyfile.in footer.html header.html \
+             opus_logo.svg trivial_example.c
+
+
+if HAVE_DOXYGEN
+
+all-local: doxygen-build.stamp
+
+doxygen-build.stamp: Doxyfile $(DOCINPUTS)
+	doxygen
+	touch $@
+
+install-data-local:
+	$(INSTALL) -d $(DESTDIR)$(docdir)/html/search
+	for f in `find html -type f \! -name "installdox"`; do	\
+		$(INSTALL_DATA) $$f $(DESTDIR)$(docdir)/$$f;	\
+	done
+
+	$(INSTALL) -d $(DESTDIR)$(mandir)/man3
+	cd man && find man3 -type f -name opus_*.3 \
+		  -exec $(INSTALL_DATA) \{} $(DESTDIR)$(mandir)/man3 \;
+
+clean-local:
+	$(RM) -r html
+	$(RM) -r latex
+	$(RM) -r man
+	$(RM) doxygen-build.stamp
+	$(RM) doxygen_sqlite3.db
+
+uninstall-local:
+	$(RM) -r $(DESTDIR)$(docdir)/html
+	$(RM) $(DESTDIR)$(mandir)/man3/opus_*.3 $(DESTDIR)$(mandir)/man3/opus.h.3
+
+endif