Add minetest.get_server_uptime() function to Lua API (#4702)

Add minetest.get_server_uptime() function to Lua API

doc/lua_api.txt

@@ -2448,6 +2448,7 @@ These functions return the leftover itemstack.
* `minetest.request_shutdown([message],[reconnect])`: request for server shutdown. Will display `message` to clients,
    and `reconnect` == true displays a reconnect button.
* `minetest.get_server_status()`: returns server status string
* `minetest.get_server_uptime()`: returns the server uptime in seconds

### Bans
* `minetest.get_ban_list()`: returns the ban list (same as `minetest.get_ban_description("")`)

src/script/lua_api/l_server.cpp

@@ -45,6 +45,15 @@ int ModApiServer::l_get_server_status(lua_State *L)
	return 1;
}

// get_server_uptime()
int ModApiServer::l_get_server_uptime(lua_State *L)
{
	NO_MAP_LOCK_REQUIRED;
	lua_pushnumber(L, getServer(L)->getUptime());
	return 1;
}


// print(text)
int ModApiServer::l_print(lua_State *L)
{
@@ -507,6 +516,7 @@ void ModApiServer::Initialize(lua_State *L, int top)
{
	API_FCT(request_shutdown);
	API_FCT(get_server_status);
	API_FCT(get_server_uptime);
	API_FCT(get_worldpath);
	API_FCT(is_singleplayer);

src/script/lua_api/l_server.h

@@ -30,6 +30,9 @@ class ModApiServer : public ModApiBase {
	// get_server_status()
	static int l_get_server_status(lua_State *L);

	// get_server_uptime()
	static int l_get_server_uptime(lua_State *L);

	// get_worldpath()
	static int l_get_worldpath(lua_State *L);

src/server.h

@@ -216,6 +216,7 @@ class Server : public con::PeerHandler, public MapEventReceiver,

	// Connection must be locked when called
	std::wstring getStatusString();
	inline double getUptime() const { return m_uptime.m_value; }

	// read shutdown state
	inline bool getShutdownRequested() const { return m_shutdown_requested; }