Improved Json record support (Gson 2.10 natively supports it) + Added ItemStack Json support

- Extract RecordTypeAdapter to its own file + only use it if Gson library does not support it (it does since 2.10, but we are unsure of which version is actually used in paper/bungee/other)
- new ItemStackAdapter to support Json (de)serializing of Bukkit ItemStack.

pandalib-paper/src/main/java/fr/pandacube/lib/paper/PandaLibPaper.java

@@ -1,5 +1,6 @@
 package fr.pandacube.lib.paper;
 
+import fr.pandacube.lib.paper.json.PaperJson;
 import fr.pandacube.lib.paper.modules.PerformanceAnalysisManager;
 import org.bukkit.plugin.Plugin;
 
@@ -9,6 +10,7 @@ public class PandaLibPaper {
 	
 	public static void onLoad(Plugin plugin) {
 		PandaLibPaper.plugin = plugin;
+		PaperJson.init();
 	}
 
 	public static void onEnable() {

pandalib-paper/src/main/java/fr/pandacube/lib/paper/json/ItemStackAdapter.java

@@ -0,0 +1,34 @@
+package fr.pandacube.lib.paper.json;
+
+import com.google.gson.JsonDeserializationContext;
+import com.google.gson.JsonDeserializer;
+import com.google.gson.JsonElement;
+import com.google.gson.JsonParseException;
+import com.google.gson.JsonSerializationContext;
+import com.google.gson.JsonSerializer;
+import com.google.gson.TypeAdapterFactory;
+import com.google.gson.internal.bind.TreeTypeAdapter;
+import com.google.gson.reflect.TypeToken;
+import org.bukkit.inventory.ItemStack;
+
+import java.lang.reflect.Type;
+import java.util.Map;
+
+/* package */ class ItemStackAdapter implements JsonSerializer<ItemStack>, JsonDeserializer<ItemStack> {
+
+    private static final TypeToken<ItemStack> ITEMSTACK_TYPE = TypeToken.get(ItemStack.class);
+    public static final TypeAdapterFactory FACTORY = TreeTypeAdapter.newFactoryWithMatchRawType(ITEMSTACK_TYPE, new ItemStackAdapter());
+
+    private static final TypeToken<Map<String, Object>> MAP_STR_OBJ_TYPE = new TypeToken<>() { };
+
+
+    @Override
+    public ItemStack deserialize(JsonElement json, Type typeOfT, JsonDeserializationContext context) throws JsonParseException {
+        return ItemStack.deserialize(context.deserialize(json, MAP_STR_OBJ_TYPE.getType()));
+    }
+
+    @Override
+    public JsonElement serialize(ItemStack src, Type typeOfSrc, JsonSerializationContext context) {
+        return context.serialize(src.serialize(), MAP_STR_OBJ_TYPE.getType());
+    }
+}

pandalib-paper/src/main/java/fr/pandacube/lib/paper/json/PaperJson.java

@@ -0,0 +1,16 @@
+package fr.pandacube.lib.paper.json;
+
+import fr.pandacube.lib.core.json.Json;
+
+/**
+ * Utility class to register Json adapters related to paper API classes.
+ */
+public class PaperJson {
+
+    /**
+     * Registers Json adapters related to paper API classes.
+     */
+    public static void init() {
+        Json.registerTypeAdapterFactory(ItemStackAdapter.FACTORY);
+    }
+}