scripting: minor logging improvements

Give scripting backends a proper name, instead of calling everything
"scripts".

Log client exit directly in client.c, as that is more general (doesn't
change actual output).

player/lua.c

@@ -1331,6 +1331,7 @@ static void add_functions(struct script_ctx *ctx)
 }
 
 const struct mp_scripting mp_scripting_lua = {
+    .name = "lua script",
     .file_ext = "lua",
     .load = load_lua,
 };