Filter out the validators absent on the classpath

[celcius112]

Hello and thank you for this great plugin,

At the moment every validators are proposed in the auto-completion, even though some of them are not present on the classpath. In this particular case, I have jcv-core but not jcv-db on the classpath:

In a perfect world, after the wars, world hunger and Covid have been eradicated, I would expect only the validators available in the core to be proposed in this particular case.