Set the game score at which the reward is shown

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From 11/8/2022 design meeting... The PhET-iO client should be able to set the game score at which the reward is shown.

TODO:

• make rewardScore a public query parameter
• add solveItScreen.model.rewardScoreProperty, initialized with EqualityExplorerQueryParameters.rewardScore
• add phetioDocumentation for rewardScoreProperty

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@amanda-phet please review.

• ?rewardScore is now a public query parameter. It must be a positive integer, and it defaults to 10. If you use an invalid value, you'll see any Oops dialog when the sim starts.
• equalityExplorer.solveItScreen.model.rewardScoreProperty is the new Property. Its initial value is the query parameter ?rewardScore. This Property can be changed via PhET-iO. It's presentation in Studio is shown below.
• Note that if you were to play 5 challenges, then set rewardScoreProperty to 4, you're never going to see a reward. A reward is given once per level, at exactly the score indicated by rewardScoreProperty.

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Deferred -- this issue will not be part of the 1.2 release, since that release will not include PhET-iO.