Specialize filterCompetitiveHits when have exact 2 clauses

[HUSTERGS]

Description

This PR propose to specialize function filterCompetitiveHits when we have exact 2 scorers, in order to reduce float calculation and potential function calls

Luceneutil result on wikimediumall with searchConcurrency=0, taskCountPerCat=5, taskRepeatCount=50 after 20 iterations

                            TaskQPS baseline      StdDevQPS my_modified_version      StdDev                Pct diff p-value
                      OrHighRare      116.59      (3.1%)      116.96      (2.7%)    0.3% (  -5% -    6%) 0.734
                       OrHighMed       87.75      (2.4%)       88.83      (2.6%)    1.2% (  -3% -    6%) 0.116
                      AndHighMed       67.91      (2.3%)       69.17      (2.2%)    1.9% (  -2% -    6%) 0.009
                     AndHighHigh       27.96      (1.4%)       28.63      (2.0%)    2.4% (  -1% -    5%) 0.000
                      OrHighHigh       26.16      (1.6%)       26.97      (1.6%)    3.1% (   0% -    6%) 0.000

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[HUSTERGS]

For what it's worth, the reason of this PR is that I find filterCompetitiveHits ocuppied about 13% of flamegraph on OrHighHigh query,

Also, filterCompetitiveHits calls MathUtil.sumUpperBound in a loop, seems repeatly calculate MathUtil.sumRelativeErrorBound(numValues), (numValues is constant within the loop), I tried to optimize this, but it shows no performance difference, maybe filterCompetitiveHits is no longer the bottleneck when numValues > 2