Proposal: Add PDO::checkLiveness method

Hi, I am the author of Swoole (https://github.com/swoole/swoole-src), I have a little network programming experience, the following is my personal opinion: I suggest not to check it, let it throw an exception (PHP8 has used exceptions as the default error reporting way). checkLiveness() is not cost-free, it will also cause redundant system call overhead, In fact, it has been heavily abused. I noticed that many PHP network programming implementations do not care about the overhead of system calls, such as constantly using recv(MSG_PEEK) to check the connection before new requests, this is how checkLiveness() works. This will cause severe performance degradation because failure is always unexpected. And it even can't guarantee that the next call is successful, the connection may be reset after check. What can you do if you noticed that the connection is disconnected? phpredis checks the connection before each request and tries to reconnect because the redis connection is almost stateless. So in phpredis, it makes some sense to do so (phpredis will retry 10 times when the connection is down, but this may be bad when the server is busy). But MySQL can't do this, the context of it is too complex, let it throw an exception, catch it, and start from the beginning again is the best and cheapest way to solve it. All in all, let it fail and try again, the overall performance will be better than checking before calling it every time, so I don't think this API is necessary. Please don't use it, it will only make your program worse. Regards, Twosee