feat(dev): File-level accepts of generated code

[kelvin-klchu]

Problem

For the current /dev experience for code review, user needs to review the entire file list of generated code, reject the changes they do not want, and then accept the remaining changes in bulk at the end.

This PR introduces improvements in user experience around the code review experience in which user can now review the file changes and accept them one at a time. User can start editing the file right away after accepting the changes without having to go through the entire generated file list.

Solution

• introduces a new action button for accepting file change for each change suggested on the file list
• accepted changes are now highlighted in green
• when accepting changes in bulk, the file list is updated to reflect the status if a change is rejected or accepted
• minor text changes / improvements

---

License: I confirm that my contribution is made under the terms of the Apache 2.0 license.

[github-actions]

• This pull request implements a feat or fix, so it must include a changelog entry (unless the fix is for an unreleased feature). Review the changelog guidelines.
  • Note: beta or "experiment" features that have active users should announce fixes in the changelog.
  • If this is not a feature or fix, use an appropriate type from the title guidelines. For example, telemetry-only changes should use the telemetry type.

[Hweinstock]

/runIntegrationTests

[nkomonen-amazon]

@kelvin-klchu could you add a changelog item

[kelvin-klchu]

rebased and added changelog