JXL: Resolution and metadata support via EXIF

- Added a class to read and write minimal exif metadata.
- JXL plugin uses EXIF metadata to load/save the resolution of the image (like GIMP).
- JXL plugin uses EXIF metadata to set/store text metadata and date/time.
- Enable info display in Dolphin (JXL File -> Properties -> Details on a JXL file, see image below).
- Enabled read test to check also image metadata and resolution.

![_52C044E4-1BA9-4D84-AC0A-B834CDAF72D8_](/uploads/f1649c2b506bf61a5f5488da0d4a4534/_52C044E4-1BA9-4D84-AC0A-B834CDAF72D8_.png){width=401 height=357}

autotests/read/jxl/gimp_exif.jxl.json

@@ -0,0 +1,19 @@
+[
+    {
+        "fileName" : "gimp_exif.png",
+        "metadata" : [
+            {
+                "Key" : "CreationDate",
+                "Value" : "2025-01-05T10:18:16"
+            },
+            {
+                "Key" : "Software" ,
+                "Value" : "GIMP 3.0.0-RC2"
+            }
+        ],
+        "resolution" : {
+            "dotsPerMeterX" : 5905,
+            "dotsPerMeterY" : 6692
+        }
+    }
+]