lloc: Count declaration statements for Cpp code

[Luni-4]

This PR fixes #614 considering declaration statements for Cpp code

[codecov-io]

Codecov Report

Merging #620 (2c16162) into master (05d71ca) will increase coverage by 0.05%.
The diff coverage is 66.66%.

@@            Coverage Diff             @@
##           master     #620      +/-   ##
==========================================
+ Coverage   53.24%   53.30%   +0.05%     
==========================================
  Files          45       45              
  Lines        3602     3617      +15     
  Branches      856      861       +5     
==========================================
+ Hits         1918     1928      +10     
  Misses       1127     1127              
- Partials      557      562       +5     

Impacted Files	Coverage Δ
src/metrics/loc.rs	77.89% <66.66%> (-0.65%)	⬇️

---

Continue to review full report at Codecov.

Legend - Click here to learn more
Δ = absolute <relative> (impact), ø = not affected, ? = missing data
Powered by Codecov. Last update 05d71ca...2c16162. Read the comment docs.

[Luni-4]

Only improvements https://community-tc.services.mozilla.com/api/queue/v1/task/dLI5m6mhRUWM94kx5zUA6w/runs/0/artifacts/public%2Fjson-diffs-and-minimal-tests.tar.gz