Analyzer refactoring: single analyzer to handle stem/no stem and stopwords

[lintool]

@chriskamphuis instead of a separate class for no-stemming, I think this is much cleaner.

@edwinzhng I think this is a much clear way to construct non-stemming analyzers, rather than the previous way.

[chriskamphuis]

So I assume this breaks Pyserini right?

[lintool]

@chriskamphuis yup - once this is merged we have to make changes to Pyserini again...

[codecov]

Codecov Report

Merging #1027 into master will increase coverage by 0.25%.
The diff coverage is 68.29%.

@@             Coverage Diff              @@
##             master    #1027      +/-   ##
============================================
+ Coverage     40.91%   41.17%   +0.25%     
- Complexity      551      560       +9     
============================================
  Files           128      127       -1     
  Lines          7659     7662       +3     
  Branches       1129     1132       +3     
============================================
+ Hits           3134     3155      +21     
+ Misses         4212     4193      -19     
- Partials        313      314       +1     

Impacted Files	Coverage Δ	Complexity Δ
...a/io/anserini/analysis/DefaultEnglishAnalyzer.java	75.00% <0.00%> (ø)	9.00% <0.00%> (?%)
...java/io/anserini/ltr/feature/CountBigramPairs.java	87.01% <0.00%> (+22.07%)	31.00% <0.00%> (+8.00%)

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[edwinzhng]

LGTM