Upgrade to fastutil 8.5.8 and fix FeatureVector bug in #840

[lintool]

Details of the bug are described in #840.

We've known about this issue for a long time, but since it has a massive impact (lots of small score changes for PRF experiments), I delayed patching until a major change. Since Lucene 8 -> 9 upgrade has already caused lots of disruption, this is a good time to fix this issue.

An additional reason: we're moving from RM3 to Rocchio as the "default" PRF technique. Good to fix before Rocchio numbers get "entrenched".

[codecov-commenter]

Codecov Report

Base: 58.30% // Head: 58.47% // Increases project coverage by +0.17% 🎉

Coverage data is based on head (630c20b) compared to base (3dfce53).
Patch coverage: 85.93% of modified lines in pull request are covered.

Additional details and impacted files

@@             Coverage Diff              @@
##             master    #1975      +/-   ##
============================================
+ Coverage     58.30%   58.47%   +0.17%     
- Complexity     1067     1084      +17     
============================================
  Files           186      186              
  Lines         10147    10161      +14     
  Branches       1398     1404       +6     
============================================
+ Hits           5916     5942      +26     
+ Misses         3758     3746      -12     
  Partials        473      473              

Impacted Files	Coverage Δ
...va/io/anserini/index/generator/TweetGenerator.java	55.78% <0.00%> (ø)
.../main/java/io/anserini/rerank/lib/Rm3Reranker.java	52.94% <25.00%> (ø)
...n/java/io/anserini/rerank/lib/RocchioReranker.java	57.79% <50.00%> (ø)
src/main/java/io/anserini/util/FeatureVector.java	97.05% <96.22%> (+14.10%)	⬆️

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