Cleanup and standardize format of changelog
Cleanup and standardize format of changelog

Using https://marketplace.visualstudio.com/items?itemName=esbenp.prettier-vscode

Change-Id: I6a9dca93d8852a606b143394318691de9890b9a3
Reviewed-on: https://dart-review.googlesource.com/c/sdk/+/206302
Auto-Submit: Kevin Moore <1d6e7d10d051cf619c5282da3c28fd8d3e0a65a4@google.com>
Reviewed-by: Bob Nystrom <afede3a9ebedb865bee78398feff6fbe97068f17@google.com>
Commit-Queue: Kevin Moore <1d6e7d10d051cf619c5282da3c28fd8d3e0a65a4@google.com>

dart-lang/sdk,dart-lang/sdk,dart-lang/sdk,dart-lang/sdk,dart-lang/sdk,dart-lang/sdk,dart-lang/sdk,dart-lang/sdk