i18n: remove the module and embed the gettext calls into the lua api

There is no need to have this as an optional module, since libintl
is a hard dependency of both PipeWire and GLib. This way we can keep
things a bit simpler and faster (no string copies and plugin lookups)

Bump meson dependency to 0.59 to benefit of the libintl lookup that
is now built into meson's dependency() function.

modules/module-lua-scripting/api/api.c

@@ -10,6 +10,7 @@
 #include <wp/wp.h>
 #include <pipewire/pipewire.h>
 #include <wplua/wplua.h>
+#include <libintl.h>
 
 #define URI_API "resource:///org/freedesktop/pipewire/wireplumber/m-lua-scripting/api.lua"
 
@@ -113,6 +114,32 @@ static const luaL_Reg source_methods[] = {
   { NULL, NULL }
 };
 
+/* i18n */
+
+static int
+i18n_gettext (lua_State *L)
+{
+  const gchar * msgid = luaL_checkstring (L, 1);
+  lua_pushstring (L, dgettext (GETTEXT_PACKAGE, msgid));
+  return 1;
+}
+
+static int
+i18n_ngettext (lua_State *L)
+{
+  const gchar * msgid = luaL_checkstring (L, 1);
+  const gchar *msgid_plural = luaL_checkstring (L, 2);
+  gulong n = luaL_checkinteger (L, 3);
+  lua_pushstring (L, dngettext (GETTEXT_PACKAGE, msgid, msgid_plural, n));
+  return 1;
+}
+
+static const luaL_Reg i18n_funcs[] = {
+  { "gettext", i18n_gettext },
+  { "ngettext", i18n_ngettext },
+  { NULL, NULL }
+};
+
 /* WpCore */
 
 static int
@@ -1434,6 +1461,9 @@ wp_lua_scripting_api_init (lua_State *L)
   luaL_newlib (L, glib_methods);
   lua_setglobal (L, "GLib");
 
+  luaL_newlib (L, i18n_funcs);
+  lua_setglobal (L, "I18n");
+
   luaL_newlib (L, log_funcs);
   lua_setglobal (L, "WpLog");