Move repository browser commit link generation into git-plugin

[uhafner]

Creation of commit links currently is done in the git-forensics plugin by accessing some internal API methods. It makes much more sense to move these methods to the git plugin itself.

This PR depends on jenkinsci/git-plugin#1034 which has been released in git-4.10.0.

[codecov]

Codecov Report

Merging #241 (a0203b7) into master (59e1897) will decrease coverage by 0.11%.
The diff coverage is 100.00%.

@@             Coverage Diff              @@
##             master     #241      +/-   ##
============================================
- Coverage     80.76%   80.64%   -0.12%     
  Complexity      162      162              
============================================
  Files            22       22              
  Lines           681      677       -4     
  Branches         73       73              
============================================
- Hits            550      546       -4     
  Misses          104      104              
  Partials         27       27              

Impacted Files	Coverage Δ
...plugins/forensics/git/util/GitCommitDecorator.java	50.00% <100.00%> (-12.50%)	⬇️

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