Make ValueSignal ignore identical values

[Legioth]

To automatically avoid some cases of infinite loops between effects, ValueSignal should fire events only if set to a value that isn't equals() with the current value. The exception is modify which should still always fire events since it's used with mutable values where the mutation means that there's no previous state to compare with.

This behavior should be mentioned in relevant JavaDocs. To further help developers realize that equality has an impact, and potentially also cover some special cases, we should provide a constructor that allows defining a custom equality checker (SerializableBiPredicate<T, T>) while using Objects::equals by default.

[mshabarov]

ValueSignal::update already has the reference equality check

T oldValue = getSignalValue();
            T newValue = updater.update(oldValue);
            if (newValue != oldValue) {
                setSignalValue(newValue);
            }

Should it be extended by equals() check as well or stay untouched?

[Legioth]

I suggest changing it to be consistent with all other similar equality checks