utils: Factor out word counting

[nijel]

Proposed changes

This makes both location use consistent implementation.

See #10278

Checklist

• Lint and unit tests pass locally with my changes.
• I have added tests that prove my fix is effective or that my feature works.
• I have added documentation to describe my feature.
• I have squashed my commits into logic units.
• I have described the changes in the commit messages.

Other information

[codecov]

Codecov Report

Merging #10279 (8685699) into main (d8e6e11) will increase coverage by 0.00%.
The diff coverage is 100.00%.

@@           Coverage Diff           @@
##             main   #10279   +/-   ##
=======================================
  Coverage   90.86%   90.86%           
=======================================
  Files         544      544           
  Lines       55862    55864    +2     
  Branches     8859     8859           
=======================================
+ Hits        50757    50760    +3     
  Misses       3548     3548           
+ Partials     1557     1556    -1     

Files	Coverage Δ
weblate/trans/models/unit.py	86.09% <100.00%> (ø)
weblate/trans/util.py	86.16% <100.00%> (+0.17%)	⬆️
weblate/trans/views/reports.py	93.19% <100.00%> (ø)

... and 1 file with indirect coverage changes