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-util/src/main/java/fr/pandacube/lib/util/BiMap.java

@@ -13,6 +13,7 @@ import java.util.function.Supplier;
  * A bi-direction map storing in a synchronized way a {@code forwardMap} that store the key to value mapping, and a
  * {@code backwardMap} that store the value to key mapping.
  * All the keys and value are always unique in this bi-directional map.
+ * This class is fully thread safe.
  * @param <K> the type of the "key"
  * @param <V> the type of the "value"
  */