MediaPlayer/Audio: fallback solution for qrc files

Not all multimedia backends allow to stream data from memory, which is necessary to play files in a qrc. As a fallback, we should copy the file to a temporary directory on disk and play from there.

Some backends already do this internally (QNX, Android). We should refactor that out and have it at the library level so backends are automatically given temporary files when they can't play the qrc file directly.

In addition to QNX and Android, AVFoundation also needs this fallback (QTBUG-36175).