macosx: Make fscontroller compatible with <10.10
This will add a fallback mechanism that uses a normal layer-backed NSView with a dark but still slightly transparent background on macOS versions that do not support NSVisualEffectView. Additionally it will allow compilation with older SDK's that have no NSVisualEffectView defined. If compiled with such an SDK, support for NSVisualEffectView is disabled completely, so even when running the compiled VLC version on 10.10 or higher it will use the old fallback view, as the SDK it was compiled with had not the necessary definitions.
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