audio/furnace: Refactor port

• Unbundle fftw3, freetype, libsndfile and portaudio (this is also more inline with other distros)
• Add USES= compiler:c++14-lang
• Remove USES= tar:xz
• Remove entries for sdl and fmt in GH_TUPLE
• Add EXTRACT_AFTER_ARGS to reduce I/O (reduces workdir size with ~40%) and as build script "leaks"
• Use CMAKE_OFF/ON/BOOL helpers
• Add patch to fix path for system rtmidi

PR: 285918