adding serialize_precision's value that uses mode2 and long double

Hi, internals. I had incorrect knowledge the serialize_precision until recently. I knew that setting this to -1 would use a long double, but I didn't know that the number of digits would not be 17. I've looked through RFC related to this. https://wiki.php.net/rfc/precise_float_value There doesn't seem to be a setting that allows you to use long double and mode2 at the same time at the moment. I think there are various methods, such as a simple method such as simply setting serialize_precision = -2, or a method of adding another new setting item. When using long doubles, it is somewhat inconvenient not to be able to display all digits with var_dump() or debug_zval_dump() when debugging. (I use the word "inconvenient" because there is probably an alternative method.) What do you think? Saki