Fix equipment slot and group API

Adds the following:
- Add test for EquipmentSlotGroup
- Expose LivingEntity#canUseSlot

Co-authored-by: SoSeDiK <mrsosedik@gmail.com>

paper-server/src/test/java/io/papermc/paper/inventory/item/EquipmentSlotGroupTest.java

@@ -0,0 +1,53 @@
+package io.papermc.paper.inventory.item;
+
+import java.lang.reflect.Field;
+import java.lang.reflect.Modifier;
+import java.util.ArrayList;
+import java.util.List;
+import net.minecraft.world.entity.EquipmentSlot;
+import org.bukkit.craftbukkit.CraftEquipmentSlot;
+import org.bukkit.inventory.EquipmentSlotGroup;
+import org.bukkit.support.environment.Normal;
+import org.junit.jupiter.params.ParameterizedTest;
+import org.junit.jupiter.params.provider.EnumSource;
+import org.junit.jupiter.params.provider.MethodSource;
+
+import static org.junit.jupiter.api.Assertions.assertEquals;
+import static org.junit.jupiter.api.Assertions.assertNotNull;
+
+@Normal
+class EquipmentSlotGroupTest {
+
+    static List<EquipmentSlotGroup> apiValues() throws ReflectiveOperationException {
+        final List<EquipmentSlotGroup> apiValues = new ArrayList<>();
+        for (final Field field : EquipmentSlotGroup.class.getDeclaredFields()) {
+            if (!Modifier.isStatic(field.getModifiers()) || !Modifier.isFinal(field.getModifiers()) || !field.getType().equals(EquipmentSlotGroup.class)) {
+                continue;
+            }
+            apiValues.add((EquipmentSlotGroup) field.get(null));
+        }
+        if (apiValues.isEmpty()) {
+            throw new RuntimeException("Didn't find any api " + EquipmentSlotGroup.class.getSimpleName());
+        }
+        return apiValues;
+    }
+
+    @ParameterizedTest
+    @MethodSource("apiValues")
+    void testBukkitToNms(final EquipmentSlotGroup slotGroup) {
+        final net.minecraft.world.entity.EquipmentSlotGroup nmsGroup = CraftEquipmentSlot.getNMSGroup(slotGroup);
+        assertNotNull(nmsGroup, "No nms slot group found for " + slotGroup);
+        assertEquals(nmsGroup.getSerializedName(), slotGroup.toString(), "slot group name mismatch");
+        for (final EquipmentSlot slot : EquipmentSlot.values()) {
+            assertEquals(nmsGroup.test(slot), slotGroup.test(CraftEquipmentSlot.getSlot(slot)));
+        }
+    }
+
+    @ParameterizedTest
+    @EnumSource(net.minecraft.world.entity.EquipmentSlotGroup.class)
+    void testNmsToBukkit(final net.minecraft.world.entity.EquipmentSlotGroup slotGroup) {
+        final EquipmentSlotGroup apiGroup = CraftEquipmentSlot.getSlot(slotGroup);
+        assertNotNull(apiGroup, "No api slot group found for " + slotGroup);
+        assertEquals(apiGroup.toString(), slotGroup.getSerializedName(), "slot group name mismatch");
+    }
+}