Optimize Dynamic#get Missing Keys

get was calling toString() on every NBT object that was ever asked for an optional
key from the object to build a string for the error text.

When done on large NBT objects, this was using a ton of computation time building the
JSON representation of the NBT object.

Now we will just skip the value when 99.9999% of the time the text is never even printed.

paper-server/patches/sources/com/mojang/serialization/Dynamic.java.patch

@@ -0,0 +1,19 @@
+--- a/com/mojang/serialization/Dynamic.java
++++ b/com/mojang/serialization/Dynamic.java
+@@ -19,6 +19,7 @@
+ 
+ @SuppressWarnings("unused")
+ public class Dynamic<T> extends DynamicLike<T> {
++    private static final boolean DEBUG_MISSING_KEYS = Boolean.getBoolean("Paper.debugDynamicMissingKeys"); // Paper - Perf: Skip toString on values like NBT
+     private final T value;
+ 
+     public Dynamic(final DynamicOps<T> ops) {
+@@ -120,7 +121,7 @@
+         return new OptionalDynamic<>(ops, ops.getMap(value).flatMap(m -> {
+             final T value = m.get(key);
+             if (value == null) {
+-                return DataResult.error(() -> "key missing: " + key + " in " + this.value);
++                return DataResult.error(() -> DEBUG_MISSING_KEYS ? "key missing: " + key + " in " + this.value : "key missing: " + key); // Paper - Perf: Skip toString on values like NBT
+             }
+             return DataResult.success(new Dynamic<>(ops, value));
+         }));