Round a quotient of a non-default mode by its remainder

[ibmibmibm]

• The divides of the non-default rounding modes dropped the remainder of the wide quotient
  before the constructor rounded it. A mode which must move away from the truncated
  quotient could not.
• The 32 and 64 bit types held five or six digits past the precision, thus the defect
  showed only when all of them were zero. The 128 bit types held zero or one digit, thus
  most quotients were wrong, and fe_dec_to_nearest_from_zero was wrong too.
• The remainder now goes in as one sticky digit after the wide quotient. The 128 bit
  divide also takes one digit more, thus the constructor has a quotient digit to round
  before the sticky digit.
• Both operands of the 128 bit divide have 34 digits, thus the quotient has at most 37
  and the block for a wider quotient was dead. It went away.

Fixes #1453

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 98.5%. Comparing base (bad17ca) to head (34b1d05).

Additional details and impacted files

@@            Coverage Diff            @@
##           develop   #1454     +/-   ##
=========================================
+ Coverage     98.4%   98.5%   +0.1%     
=========================================
  Files          300     301      +1     
  Lines        25188   25223     +35     
  Branches      2189    2189             
=========================================
+ Hits         24774   24832     +58     
+ Misses         414     391     -23     

Files with missing lines	Coverage Δ
include/boost/decimal/detail/div_impl.hpp	91.7% <100.0%> (+11.9%)	⬆️
test/github_issue_1453.cpp	100.0% <100.0%> (ø)

... and 2 files with indirect coverage changes

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