[GR-64965] Do not try to validate type state propagation into disabled flows

[graalvmbot]

When TypeFlow.validateFixedPointState tries to propagate type state from a flow to its uses, it should only do so if the use is enabled, because the saturation callback methods onInputSaturated and onObservedSaturated are only registered but not executed for disabled flows. Their execution is delayed until the flow becomes enabled. Therefore, TypeFlow.processInputState, which in some cases (e.g. conditional flow) explicitly queries the state of its inputs and observees) might return a bigger value compared to the original state of the flow, which is actually valid behaviour in this case (as the saturation callbacks that can change the type state of the flow were not yet executed, because it is not enabled). We should therefore only try to propagate values into already enabled flows in the type flow graph validation.