[CSM] Add flavour limits controlled by server (#5930)

* [CSM] Add flavour limits controlled by server

Server send flavour limits to client permitting to disable or limit some Lua calls

* Add limits for reading nodedefs and itemdefs

* flavour: Add lookup node limits

* Merge get_node_or_nil into get_node.

Sending fake node doesn't make sense in CSM, just return nil if node is not available for any reason

* Add node range customization when noderange flavour is enabled (default 8 nodes)

* Limit nodes range & disable chat message sending by default

* Bump protocol version

minetest.conf.example

@@ -1172,6 +1172,19 @@
 #    type: bool
 # server_side_occlusion_culling = true
 
+#    Restricts the access of certain client-side functions on servers
+#    Combine these byteflags below to restrict more client-side features:
+#    LOOKUP_NODES_LIMIT: 1 (limits get_node call client-side to csm_flavour_noderange_limit)
+#    CHAT_MESSAGES: 2 (disable send_chat_message call client-side)
+#    READ_ITEMDEFS: 4 (disable get_item_def call client-side)
+#    READ_NODEDEFS: 8 (disable get_node_def call client-side)
+#    type: int
+# csm_flavour_limits = 3
+
+#   If the CSM flavour for node range is enabled, get_node is limited to
+#   this many nodes from the player.
+# csm_flavour_noderange_limit 8
+
 ## Mapgen
 
 #    Name of map generator to be used when creating a new world.