[READY] Make vimsupport.BuildRange construct a half-open range

[bstaletic]

PR Prelude

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Why this change is necessary and useful

The rest of YCM is already dealing with half-open ranges and so does LSP.
In fact, ycmd assumes this is a half-open range, so YCM had a bug.

Though I have to look at what non-LSP completers are doing.

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This change is 

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 89.80%. Comparing base (63ab13e) to head (b31f3db).

Additional details and impacted files

@@            Coverage Diff             @@
##           master    #4266      +/-   ##
==========================================
- Coverage   89.95%   89.80%   -0.15%     
==========================================
  Files          37       37              
  Lines        4758     4758              
==========================================
- Hits         4280     4273       -7     
- Misses        478      485       +7     

[puremourning]