8236073: G1: Use SoftMaxHeapSize to guide GC heuristics

*** 182,192 ****
    // update the derived pointer table.
    update_derived_pointers();
  
    BiasedLocking::restore_marks();
  
!   _heap->prepare_heap_for_mutators();
  
    _heap->policy()->record_full_collection_end();
    _heap->gc_epilogue(true);
  
    _heap->verify_after_full_collection();
--- 182,192 ----
    // update the derived pointer table.
    update_derived_pointers();
  
    BiasedLocking::restore_marks();
  
!   _heap->prepare_heap_for_mutators(scope()->is_explicit_gc());
  
    _heap->policy()->record_full_collection_end();
    _heap->gc_epilogue(true);
  
    _heap->verify_after_full_collection();