Fix text components in signs not being rewritten in the 1.21.7→1.21.5 step

This was causing connection crashes for versions ≤1.21.4, since the
1.21.5.→1.21.4 step rewrites all text components as strings, and thus
parses the NBT.
Since custom click events (and dialogs) were not being filtered on
signs in the 1.21.6→1.21.5 step (despite being correctly handled
everywhere else since ViaVersion#1108), the latter step was failing to properly
read the NBT structure and thus crashing the player's connection.

The fix was done by lifting the sign logic in
`BlockItemPacketRewriter1_21_5` and adapting it into
`BlockItemPacketRewriter1_21_6`. All filtering is still delegated to the
appropriate `ComponentRewriter`, so required code change was rather
small.

This commit is almost identical to my other fix related to sprites in
the 1.21.9→1.21.7 step. See commit d273b06 (e3a4761) and PR ViaVersion#1147.

Fixes ViaVersion#1172

Author: Tmpod

common/src/main/java/com/viaversion/viabackwards/protocol/v1_21_6to1_21_5/rewriter/BlockItemPacketRewriter1_21_6.java

@@ -22,6 +22,7 @@
 import com.viaversion.viabackwards.api.rewriters.BackwardsStructuredItemRewriter;
 import com.viaversion.viabackwards.protocol.v1_21_6to1_21_5.Protocol1_21_6To1_21_5;
 import com.viaversion.viaversion.api.connection.UserConnection;
+import com.viaversion.viaversion.api.minecraft.blockentity.BlockEntity;
 import com.viaversion.viaversion.api.minecraft.data.StructuredDataContainer;
 import com.viaversion.viaversion.api.minecraft.data.StructuredDataKey;
 import com.viaversion.viaversion.api.minecraft.item.Item;
@@ -40,6 +41,8 @@
 import static com.viaversion.viaversion.protocols.v1_21_5to1_21_6.rewriter.BlockItemPacketRewriter1_21_6.upgradeItemData;
 
 public final class BlockItemPacketRewriter1_21_6 extends BackwardsStructuredItemRewriter<ClientboundPacket1_21_6, ServerboundPacket1_21_5, Protocol1_21_6To1_21_5> {
+    private static final int SIGN_BOCK_ENTITY_ID = 7;
+    private static final int HANGING_SIGN_BOCK_ENTITY_ID = 8;
 
     public BlockItemPacketRewriter1_21_6(final Protocol1_21_6To1_21_5 protocol) {
         super(protocol);
@@ -52,8 +55,8 @@ public void registerPackets() {
         blockRewriter.registerBlockUpdate(ClientboundPackets1_21_6.BLOCK_UPDATE);
         blockRewriter.registerSectionBlocksUpdate1_20(ClientboundPackets1_21_6.SECTION_BLOCKS_UPDATE);
         blockRewriter.registerLevelEvent1_21(ClientboundPackets1_21_6.LEVEL_EVENT, 2001);
-        blockRewriter.registerLevelChunk1_19(ClientboundPackets1_21_6.LEVEL_CHUNK_WITH_LIGHT, ChunkType1_21_5::new);
-        blockRewriter.registerBlockEntityData(ClientboundPackets1_21_6.BLOCK_ENTITY_DATA);
+        blockRewriter.registerLevelChunk1_19(ClientboundPackets1_21_6.LEVEL_CHUNK_WITH_LIGHT, ChunkType1_21_5::new, this::handleBlockEntity);
+        blockRewriter.registerBlockEntityData(ClientboundPackets1_21_6.BLOCK_ENTITY_DATA, this::handleBlockEntity);
 
         protocol.registerClientbound(ClientboundPackets1_21_6.SET_CURSOR_ITEM, this::passthroughClientboundItem);
         registerSetPlayerInventory(ClientboundPackets1_21_6.SET_PLAYER_INVENTORY);
@@ -149,4 +152,29 @@ protected void restoreBackupData(final Item item, final StructuredDataContainer
             ));
         }
     }
+
+    private void handleBlockEntity(final UserConnection connection, final BlockEntity blockEntity) {
+        final CompoundTag tag = blockEntity.tag();
+        if (tag == null) {
+            return;
+        }
+
+        if (blockEntity.typeId() == SIGN_BOCK_ENTITY_ID || blockEntity.typeId() == HANGING_SIGN_BOCK_ENTITY_ID) {
+            updateSignMessages(connection, tag.getCompoundTag("front_text"));
+            updateSignMessages(connection, tag.getCompoundTag("back_text"));
+        }
+    }
+
+    private void updateSignMessages(final UserConnection connection, final CompoundTag tag) {
+        if (tag == null) {
+            return;
+        }
+
+        final ListTag<?> messages = tag.getListTag("messages");
+        protocol.getComponentRewriter().processTag(connection, messages);
+        final ListTag<?> filteredMessages = tag.getListTag("filtered_messages");
+        if (filteredMessages != null) {
+            protocol.getComponentRewriter().processTag(connection, filteredMessages);
+        }
+    }
 }