Added more efficient code for DiceRollerFinal

[ps428]

In this code, instead of using lateinit, I have modified the rollDice function, so that it has an input parameter of type ImageView, when we call this function in line 45, I have called the diceImage variable that is of type ImageView and "points to" the @id/dice_image.

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[ps428]

@googlebot I signed it!