Convert functions between duration and ignition::time

[ahcorde]

As discussed in the PR gazebosim/gz-sensors#41 (comment) makes sense to use duration instead of time_point, This function will convert secs and nanoseconds to std::chrono::steady_clock::duration

This PR is part of this issue gazebosim/gz-common#61.

Signed-off-by: ahcorde [email protected]

[codecov]

Codecov Report

Merging #85 into master will increase coverage by 0.01%.
The diff coverage is 100.00%.

@@            Coverage Diff             @@
##           master      #85      +/-   ##
==========================================
+ Coverage   85.83%   85.85%   +0.01%     
==========================================
  Files           7        7              
  Lines         805      806       +1     
==========================================
+ Hits          691      692       +1     
  Misses        114      114              

Impacted Files	Coverage Δ
src/Utility.cc	83.73% <100.00%> (+0.02%)	⬆️

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[chapulina]

I think we could keep the old functions, but since this is ready to go I don't think it needs to change. I'd just ask that the style comment below be fixed before merging 😉