fix memory management issue in MVKSwapchain

[NekoAsakura]

#2399
Fix memory management issue in MVKSwapchain

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[gnattu]

I'm afraid this change alone is not enough to fix the problem described in #2399. It appears that CAEDRMetadata is also a managed objc object which the autorelease pool might trying to release and still cause the double free crash. Chromium does not do explicit release on this object and I think we should do the same.

This is already reproducible by using mpv with gpu-next and target-colorspace-hint=yes, play an HDR file, enter the full screen then quit the full screen, then close the player, you would see a segfault. This segfault disappears after removing the explicit release of CAEDRMetadata