Make bcmath functions more strict

Hello everyone! Recently I noticed that there are strange behavior going on if I use bcmath functions (some examples you can see here https://3v4l.org/D3s7J). I also previously had little discussion with Sara Golemon on twitter about this (https://twitter.com/SaraMG/status/1087902930110480384). So to conclude things that I want, is drop behavior (they should throw invalid argument exception) that I've showed in the first link and as Sara suggested add deprecation warning (but I think it should be E_NOTICE level errors) in 7.4. ------ Vladyslav Startsev