Add support for ISO-15924 abbreviation script code to locale_data

[Flamefire]

The value is (currently) ignored but this allows to parse locale names returned by ICU.

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 95.84%. Comparing base (a996b00) to head (1d85ae3).
Report is 1 commits behind head on develop.

Additional details and impacted files

@@             Coverage Diff             @@
##           develop     #245      +/-   ##
===========================================
+ Coverage    95.81%   95.84%   +0.02%     
===========================================
  Files          117      117              
  Lines        10352    10410      +58     
===========================================
+ Hits          9919     9977      +58     
  Misses         433      433              

Files with missing lines	Coverage Δ
include/boost/locale/util/locale_data.hpp	100.00% <100.00%> (ø)
src/boost/locale/util/locale_data.cpp	100.00% <100.00%> (ø)
test/test_util.cpp	100.00% <100.00%> (ø)

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