8200730: Fix debug=gc+phases time tracking in Remark and Cleanup Summary: Timing in Remark and Cleanup pauses did not use instance variables for the scoped timing objects, so these durations were always zero. Reviewed-by: sangheki, sjohanss

8200426: Make G1 code use _g1h members Summary: Consistently use _g1h member names for cached G1CollectedHeap* variables. Reviewed-by: sangheki, sjohanss