Mac Screensharing: Avoid to block filter while requesting permission. Also, allow to stop the thread while doing it.

- Make Filter following default device.
- Add "Default Capture"/"Default Playback" cards.
- Fix muted devices where sample rate is not managed by Audio unit.
- Factorization on getting default device, sample rate, notifications.
- Add [MSAU] debug flag and fix message typos.

Load OpenGLs libraries only if needed and check for QT6 open libraries for a software implementation fallback.
Make optional EGL to avoid incompatibilities with Qt5/6 and systems libraries.
Split libraries load and function initializations.

and C++ refactor

Fix unchecked 'output2' null pointer that can cause crashes when using the video_preview_stream_start().

Add a randomness part to rtcp report interval, to avoid synchronized RTCP by each party sending during tests.

ECC: update the framesize of the audio signal to analyze in tone detector, depending on the chosen sampling rate. The audio sample duration is then always 20 ms.