Fix Spigot annotation mistakes

while some of these may of been true, they are extreme cases and cause
a ton of noise to plugin developers.

Use ApiStatus.Internal instead of Deprecated for actual internal API
that continues to have use (internally).

These do not help plugin developers if they bring moise noise than value.

paper-api/src/main/java/org/bukkit/entity/ItemDisplay.java

@@ -14,7 +14,7 @@ public interface ItemDisplay extends Display {
      *
      * @return the displayed item stack
      */
-    @Nullable
+    @NotNull // Paper
     ItemStack getItemStack();
 
     /**