Implement getChanges() for GHEventPayload.GHIssueComment and GHEventPayload.PullRequestReviewComment

[willtsai]

Description

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Fixes #1243

[willtsai]

Note: I chose to implement with a single GHCommentChanges.java wrapper class since the Webhook payload for both issue comments change and pull request review comment changes are identical, e.g.

  "changes": {
    "body": {
      "from": "pull request comment BEFORE edit"
    }
  },

[codecov]

Codecov Report

Merging #1322 (cf6ded0) into main (d576643) will increase coverage by 0.02%.
The diff coverage is 100.00%.

@@             Coverage Diff              @@
##               main    #1322      +/-   ##
============================================
+ Coverage     78.15%   78.17%   +0.02%     
  Complexity     2045     2045              
============================================
  Files           200      200              
  Lines          6277     6283       +6     
  Branches        356      356              
============================================
+ Hits           4906     4912       +6     
  Misses         1162     1162              
  Partials        209      209              

Impacted Files	Coverage Δ
...c/main/java/org/kohsuke/github/GHEventPayload.java	80.41% <100.00%> (+0.50%)	⬆️

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[willtsai]

Committed changes to move CommentChanges into static class within GHEventPayload. Please review again, thanks!