Fix unit test on mac.

This add requirement for mac os 10.5 minimum.

unit tests require to run against the freshly compiled non-installed library.
To do so, it makes use of rpath functionality. However, on mac rpath behaves differently and require to modify the library install_path value and amend @rpath to it

Update external libraries to be compiled in the same fashion.
Add AudioOutputUtil::InterleaveSamples method.

Will allow to convert planar audio into interleaved. Currently using FFmpeg's SWR_CONVERT which has a much more extensive range of capabilities.
AudioOutputUtil::InterleaveSamples doesn't need to allocate memory, and is much faster and simpler for this straightforward task.
Add AudioOutputSettings::AVSampleFormatToFormat API.

As name suggests
Update AudioOutputUtil::DecodeAudio to use new API
Update AVFD to use new AudioOutputSettings::AVSampleFormatToFormat
Update mythmusic avfd to use new AudioOutputSettings::AVSampleFormatToFormat