mac/vulkan: log EDR changes of metal layer

since we have a mapping layer between vulkan and metal (MoltenVK) we
don't actually know which EDR data is used/mapped to.

log EDR data changes to actually see which EDR data was chosen.

video/out/mac/metal_layer.swift

@@ -52,6 +52,14 @@ class MetalLayer: CAMetalLayer {
         }
     }
 
+    override var edrMetadata: CAEDRMetadata? {
+        didSet {
+            if edrMetadata != oldValue {
+                log.verbose("Metal layer HDR metadata changed: \(edrMetadata?.description ?? "nil")")
+            }
+        }
+    }
+
     init(common com: MacCommon) {
         common = com
         super.init()