Fix getUsageMethod bug introduced by #979

[bqth29]

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• Tests for the changes have been added (for bug fixes / features)
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What is the new behavior (if this is a feature change)?
PR #979 introduced an optimized way of retrieving a remedial action's usage rule for a given state. However, for onConstraint usage rules, in the computeUsageMethodPerStateAndInstant method, the following check was missing before to upate the state to usage rule map:

if (usageRule.getInstant().equals(state.getInstant())) {
    updateMapWithValue(usageMethodPerState, state, usageRule.getUsageMethod());
}

This check is necessary to remain equivalent to UsageRule::getUsageMethod(State state)