log: add Handler getter to Logger interface

[ucwong]

log: Add Handler getter to Logger interface

[codecov]

Codecov Report

Attention: Patch coverage is 0% with 5 lines in your changes are missing coverage. Please review.

Project coverage is 47.28%. Comparing base (3793419) to head (cda7391).
Report is 41 commits behind head on master.

Additional details and impacted files

@@            Coverage Diff             @@
##           master    #1960      +/-   ##
==========================================
+ Coverage   47.24%   47.28%   +0.04%     
==========================================
  Files         568      568              
  Lines       68860    68864       +4     
==========================================
+ Hits        32531    32561      +30     
+ Misses      33803    33774      -29     
- Partials     2526     2529       +3     

Files	Coverage Δ
log/logger.go	31.03% <0.00%> (-0.74%)	⬇️
internal/testlog/testlog.go	70.87% <0.00%> (-1.41%)	⬇️

... and 8 files with indirect coverage changes