Streamline logic of create_distribution_table utility and improve tbi fuzzing

[martinholmer]

This pull request adds a decile_details argument to the add_quantile_row_table_variable utility function.
The remaining changes all flow from that change:

1. The logic of the create_distribution_table utility has been considerably simplified and made more accurate.
2. The fuzzing of distribution table PUF results in the TaxBrain Interface (tbi) has been strengthened by fuzzing each of the subgroups of the bottom and top deciles (rather than fuzzing just the whole bottom decile and the whole top decile).

[codecov-io]

Codecov Report

Merging #1972 into master will not change coverage.
The diff coverage is 100%.

@@          Coverage Diff           @@
##           master   #1972   +/-   ##
======================================
  Coverage     100%    100%           
======================================
  Files          38      38           
  Lines        3780    3783    +3     
======================================
+ Hits         3780    3783    +3

Impacted Files	Coverage Δ
taxcalc/taxcalcio.py	100% <ø> (ø)	⬆️
taxcalc/utils.py	100% <100%> (ø)	⬆️

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