Fix chunk unloading regression from upstream merge

Commit a24318ee changed drop() to immediately remove chunks from cache,
bypassing the deferred m_toDrop save/unload pipeline. This caused missing
chunks on dedicated servers, iterator invalidation in dropAll() and
ServerLevel::save(), and entity duplication (item frames) from chunks
being reloaded without their entities first being removed from the level.

- ServerChunkCache::drop(): restore m_toDrop queue instead of immediate
  cache removal, so tick() can save/unload/move to unloadedCache safely
- MultiPlayerChunkCache::drop(): restore soft-unload (keep chunk in cache
  with loaded=true) instead of nulling cache and hasData
- PlayerChunkMap::setRadius(): remove dropAll() call when reducing radius,
  the per-chunk removal loop already handles out-of-range chunks

Minecraft.Client/MultiPlayerChunkCache.cpp

@@ -150,15 +150,14 @@ void MultiPlayerChunkCache::drop(const int x, const int z)
 
 	if (chunk != nullptr && !chunk->isEmpty())
 	{
-		// Unload chunk but keep tile entities
+		// Drop entities in the chunks, especially for the case when a player is dead
+		// as they will not get the RemoveEntity packet if an entity is removed.
+		// Don't delete tile entities, as they won't get recreated unless they've got
+		// update packets. Tile entities are created on the client by the chunk rebuild.
 		chunk->unload(false);
 
-		const auto it = std::find(loadedChunkList.begin(), loadedChunkList.end(), chunk);
-		if (it != loadedChunkList.end()) loadedChunkList.erase(it);
-
-		cache[idx] = nullptr;
-		hasData[idx] = false;
-		chunk->loaded = false;
+		// Keep chunk in cache with structural data intact.
+		chunk->loaded = true;
 	}
 }