8047328: Improve memory usage for cards in SparsePRTEntry Summary: Use uint16_t for cards in a SparsePRTEntry, and use an additional integer to record the current position on where to add the next card. Reviewed-by: mgerdin, ehelin Contributed-by: Andreas Sjoberg <andreas.sjoberg@oracle.com>, Thomas Schatzl <thomas.schatzl@oracle.com>

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