Cherry-pick 31c43b7. rdar://125620290

    [WebXR] Depth values are not correct
    https://bugs.webkit.org/show_bug.cgi?id=272119
    <radar://125620290>

    Reviewed by Dan Glastonbury.

    Compositor expects reverse-Z but WebXR writes forward Z values, so
    just zero them for now so the reprojection doesn't cause jittering.

    * Source/WebCore/Modules/webxr/WebXROpaqueFramebuffer.cpp:
    (WebCore::WebXROpaqueFramebuffer::blitSharedToLayered):

    Canonical link: https://commits.webkit.org/277040@main

Canonical link: https://commits.webkit.org/276863.10@safari-7619.1.8-branch

Source/WebCore/Modules/webxr/WebXROpaqueFramebuffer.cpp

@@ -320,6 +320,10 @@ void WebXROpaqueFramebuffer::blitSharedToLayered(GraphicsContextGL& gl)
 
         gl.blitFramebuffer(horizontalOffset, verticalOffset, horizontalOffset + adjustedWidth, verticalOffset + adjustedHeight, 0, 0, adjustedWidth, adjustedHeight, buffers, GL::NEAREST);
 
+        // FIXME: https://bugs.webkit.org/show_bug.cgi?id=272104 - [WebXR] Compositor expects reverse-Z values
+        gl.clearDepth(FLT_MIN);
+        gl.clear(GL::DEPTH_BUFFER_BIT | GL::STENCIL_BUFFER_BIT);
+
         phyiscalSize = m_rightPhysicalSize;
         viewport = m_rightViewport;
     }