Add player:get_meta(), deprecate player attributes (#7202)

* Add player:get_meta(), deprecate player attributes

src/script/lua_api/l_playermeta.h

@@ -0,0 +1,57 @@
+/*
+Minetest
+Copyright (C) 2013 celeron55, Perttu Ahola <celeron55@gmail.com>
+Copyright (C) 2017-8 rubenwardy <rw@rubenwardy.com>
+
+This program is free software; you can redistribute it and/or modify
+it under the terms of the GNU Lesser General Public License as published by
+the Free Software Foundation; either version 2.1 of the License, or
+(at your option) any later version.
+
+This program is distributed in the hope that it will be useful,
+but WITHOUT ANY WARRANTY; without even the implied warranty of
+MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+GNU Lesser General Public License for more details.
+
+You should have received a copy of the GNU Lesser General Public License along
+with this program; if not, write to the Free Software Foundation, Inc.,
+51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA.
+*/
+
+#pragma once
+
+#include "lua_api/l_base.h"
+#include "lua_api/l_metadata.h"
+#include "irrlichttypes_bloated.h"
+#include "inventory.h"
+#include "metadata.h"
+
+class PlayerMetaRef : public MetaDataRef
+{
+private:
+	Metadata *metadata = nullptr;
+
+	static const char className[];
+	static const luaL_Reg methods[];
+
+	static PlayerMetaRef *checkobject(lua_State *L, int narg);
+
+	virtual Metadata *getmeta(bool auto_create);
+
+	virtual void clearMeta();
+
+	virtual void reportMetadataChange();
+
+	// garbage collector
+	static int gc_object(lua_State *L);
+
+public:
+	PlayerMetaRef(Metadata *metadata) : metadata(metadata) {}
+	~PlayerMetaRef() = default;
+
+	// Creates an ItemStackMetaRef and leaves it on top of stack
+	// Not callable from Lua; all references are created on the C side.
+	static void create(lua_State *L, Metadata *metadata);
+
+	static void Register(lua_State *L);
+};