Add Material Tags

This adds a bunch of useful and missing Tags to be able to identify items that
are related to each other by a trait.

Co-authored-by: Jake Potrebic <jake.m.potrebic@gmail.com>
Co-authored-by: Lena Kolb <lenakolb2204@gmail.com>
Co-authored-by: Layla Silbernberg <livsilbernberg@gmail.com>
Co-authored-by: Newwind <newwindserver@gmail.com>

paper-api/src/test/java/com/destroystokyo/paper/MaterialTagsTest.java

@@ -0,0 +1,58 @@
+/*
+ * Copyright (c) 2018 Daniel Ennis (Aikar) MIT License
+ */
+
+package com.destroystokyo.paper;
+
+import io.papermc.paper.tag.BaseTag;
+import io.papermc.paper.tag.EntityTags;
+import java.lang.reflect.Field;
+import java.lang.reflect.Modifier;
+import java.util.HashSet;
+import java.util.Set;
+import java.util.logging.Level;
+import org.bukkit.Bukkit;
+import org.bukkit.support.AbstractTestingBase;
+import org.junit.jupiter.api.Test;
+
+import static org.junit.jupiter.api.Assertions.assertTrue;
+
+public class MaterialTagsTest extends AbstractTestingBase {
+
+    @Test
+    public void testInitialize() {
+        try {
+            MaterialTags.SHULKER_BOXES.getValues();
+            assert true;
+        } catch (Throwable e) {
+            Bukkit.getLogger().log(Level.SEVERE, e.getMessage(), e);
+            assert false;
+        }
+    }
+
+    @Test
+    public void testLocked() {
+        testLocked(MaterialTags.class);
+        testLocked(EntityTags.class);
+    }
+
+    private static void testLocked(Class<?> clazz) {
+        for (BaseTag<?, ?> tag : collectTags(clazz)) {
+            assertTrue(tag.isLocked(), "Tag " + tag.key() + " is not locked");
+        }
+    }
+
+    private static Set<BaseTag<?, ?>> collectTags(Class<?> clazz) {
+        Set<BaseTag<?, ?>> tags = new HashSet<>();
+        try {
+            for (Field field : clazz.getDeclaredFields()) {
+                if (Modifier.isStatic(field.getModifiers()) && Modifier.isFinal(field.getModifiers()) && BaseTag.class.isAssignableFrom(field.getType())) {
+                    tags.add((BaseTag<?, ?>) field.get(null));
+                }
+            }
+        } catch (IllegalAccessException e) {
+            e.printStackTrace();
+        }
+        return tags;
+    }
+}

paper-api/src/test/java/io/papermc/paper/EntityTagsTest.java

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+package io.papermc.paper;
+
+import io.papermc.paper.tag.EntityTags;
+import java.util.logging.Level;
+import org.bukkit.Bukkit;
+import org.bukkit.support.AbstractTestingBase;
+import org.junit.jupiter.api.Test;
+
+public class EntityTagsTest extends AbstractTestingBase {
+
+    @Test
+    public void testInitialize() {
+        try {
+            EntityTags.HORSES.getValues();
+            assert true;
+        } catch (Throwable e) {
+            Bukkit.getLogger().log(Level.SEVERE, e.getMessage(), e);
+            assert false;
+        }
+    }
+}