Calculates the top index based on the current vertical scroll offset. The top index is the index of the topmost fully visible line or the topmost partially visible line if no line is fully visible. The top index starts at 0.
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Calculates the top index based on the current vertical scroll offset. The top index is the index of the topmost fully visible line or the topmost partially visible line if no line is fully visible. The top index starts at 0.