lib: refactor PriorityQueue to use private field - #43889

                                                             confidence improvement accuracy (*)    (**)   (***)
timers/immediate.js type='breadth1' n=5000000                               -1.35 %       ±3.56%  ±4.73%  ±6.17%
timers/immediate.js type='breadth4' n=5000000                                4.02 %       ±4.31%  ±5.73%  ±7.47%
timers/immediate.js type='breadth' n=5000000                                 0.42 %       ±5.39%  ±7.18%  ±9.37%
timers/immediate.js type='clear' n=5000000                                   2.11 %       ±2.44%  ±3.25%  ±4.24%
timers/immediate.js type='depth1' n=5000000                                 -0.42 %       ±1.17%  ±1.56%  ±2.03%
timers/immediate.js type='depth' n=5000000                                   0.39 %       ±1.42%  ±1.89%  ±2.47%
timers/set-immediate-breadth-args.js n=5000000                              -1.76 %       ±3.17%  ±4.22%  ±5.49%
timers/set-immediate-breadth.js n=10000000                                  -0.44 %       ±2.97%  ±3.95%  ±5.14%
timers/set-immediate-depth-args.js n=5000000                                 0.74 %       ±1.58%  ±2.10%  ±2.73%
timers/timers-breadth-args.js n=1000000                                      1.91 %       ±2.86%  ±3.81%  ±4.96%
timers/timers-breadth.js n=5000000                                           1.35 %       ±5.18%  ±6.91%  ±9.03%
timers/timers-cancel-pooled.js n=5000000                                     4.68 %      ±10.73% ±14.27% ±18.58%
timers/timers-cancel-unpooled.js direction='end' n=1000000                   1.86 %      ±17.91% ±23.83% ±31.02%
timers/timers-cancel-unpooled.js direction='start' n=1000000                -1.81 %       ±8.76% ±11.67% ±15.19%
timers/timers-depth.js n=1000                                               -0.04 %       ±0.32%  ±0.42%  ±0.55%
timers/timers-insert-pooled.js n=5000000                                     0.17 %       ±4.17%  ±5.55%  ±7.22%
timers/timers-insert-unpooled.js direction='end' n=1000000                   2.70 %       ±4.96%  ±6.60%  ±8.59%
timers/timers-insert-unpooled.js direction='start' n=1000000                -0.65 %       ±3.91%  ±5.20%  ±6.79%
timers/timers-timeout-nexttick.js n=50000                                    0.20 %       ±3.12%  ±4.15%  ±5.41%
timers/timers-timeout-nexttick.js n=5000000                                  5.75 %       ±6.79%  ±9.04% ±11.77%
timers/timers-timeout-pooled.js n=10000000                                   9.33 %      ±10.21% ±13.59% ±17.70%
timers/timers-timeout-unpooled.js n=1000000                                 -1.45 %       ±8.84% ±11.77% ±15.33%

Be aware that when doing many comparisons the risk of a false-positive
result increases. In this case, there are 22 comparisons, you can thus
expect the following amount of false-positive results:
  1.10 false positives, when considering a   5% risk acceptance (*, **, ***),
  0.22 false positives, when considering a   1% risk acceptance (**, ***),
  0.02 false positives, when considering a 0.1% risk acceptance (***)

                                confidence improvement accuracy (*)   (**)  (***)
util/priority-queue.js n=100000                -2.50 %       ±4.41% ±5.87% ±7.64%

Be aware that when doing many comparisons the risk of a false-positive
result increases. In this case, there are 1 comparisons, you can thus
expect the following amount of false-positive results:
  0.05 false positives, when considering a   5% risk acceptance (*, **, ***),
  0.01 false positives, when considering a   1% risk acceptance (**, ***),
  0.00 false positives, when considering a 0.1% risk acceptance (***)