Cherry-pick e021db3. rdar://125019855

    REGRESSION (276177@main): LinearMediaPlayer controls briefly appear when entering element fullscreen
    https://bugs.webkit.org/show_bug.cgi?id=271251
    rdar://125019855

    Reviewed by Jer Noble.

    On platforms that support fullscreen standby, VideoPresentationInterface::setupFullscreen() is
    called (with `standby` set to true) when element fullscreen is activated for an element containing
    a <video> descendant. This prewarms the presentation interface so that's it's ready to enter
    picture-in-picture if requested.

    After 276177@main, this prewarming inserts a LMKPlayableViewController in the WKWebView's hierarchy.
    Even though the VC's root view's `hidden` property is set to YES, due to a bug in LinearMediaKit
    parts of the media controls remain visible for a brief period. To work around this bug, since
    visionOS does not support automatic picture-in-picture we can just disable support for fullscreen
    standby. This avoids calls to VideoPresentationInterface::setupFullscreen() when entering element
    fullscreen.

    * Source/WebKit/WebProcess/cocoa/VideoPresentationManager.mm:
    (WebKit::VideoPresentationManager::supportsVideoFullscreenStandby const):

    Canonical link: https://commits.webkit.org/276364@main

Identifier: 276246.6@safari-7619.1.6-branch

Source/WebKit/WebProcess/cocoa/VideoPresentationManager.mm

@@ -281,7 +281,7 @@ static FloatRect inlineVideoFrame(HTMLVideoElement& element)
 
 bool VideoPresentationManager::supportsVideoFullscreenStandby() const
 {
-#if PLATFORM(IOS_FAMILY)
+#if PLATFORM(IOS_FAMILY) && !PLATFORM(VISION)
     return true;
 #else
     return false;