Add new ContentParamType2 "CPT2_DEGROTATE"

This might break some mods, but it is important for all uses of the param2 to
be documented.

This doesn't need a serialisation version or network protocol version change,
as old clients will still work on new servers, and it is bearable to have
new clients getting non rotated plants on old servers.

src/script/cpp_api/s_node.cpp

@@ -57,6 +57,7 @@ struct EnumString ScriptApiNode::es_ContentParamType2[] =
 		{CPT2_FACEDIR, "facedir"},
 		{CPT2_WALLMOUNTED, "wallmounted"},
 		{CPT2_LEVELED, "leveled"},
+		{CPT2_DEGROTATE, "degrotate"},
 		{0, NULL},
 	};