feat: create new MR diff comments

This MR introduces a feature that allows users to comment on MR diff. It removes feature flag so the commenting ranges are visible by default.

adding-new-comments-on-diff

Error handling

new-comment-error

In a case that the extension fails to create a comment (e.g. network failure), we show the user a message and store the comment text in the log. The comment is not lost, but it's not trivial to try to resend the comment.

{
  "userMessage": "Extension failed to create the comment.\n         Open extension logs to see your comment text and find more details about the error",
  "errorMessage": "MR(77670491), {\"baseSha\":\"1f0fa02de1f6b913d674a8be10899fb8540237a9\",\"headSha\":\"ee2c4f1b9e07894d896c247c24858bc513e3a53b\",\"startSha\":\"1f0fa02de1f6b913d674a8be10899fb8540237a9\",\"paths\":{\"oldPath\":\"test.js\",\"newPath\":\"test.js\"},\"oldLine\":8,\"newLine\":8}, FetchError: request to https://gitlab.com/api/graphql failed, reason: getaddrinfo ENOTFOUND gitlab.com",
  "stack": [
    "Error: MR(77670491), {\"baseSha\":\"1f0fa02de1f6b913d674a8be10899fb8540237a9\",\"headSha\":\"ee2c4f1b9e07894d896c247c24858bc513e3a53b\",\"startSha\":\"1f0fa02de1f6b913d674a8be10899fb8540237a9\",\"paths\":{\"oldPath\":\"test.js\",\"newPath\":\"test.js\"},\"oldLine\":8,\"newLine\":8}, FetchError: request to https://gitlab.com/api/graphql failed, reason: getaddrinfo ENOTFOUND gitlab.com",
    "\tat GitLabNewService.<anonymous> (/Users/tomas/workspace/gitlab-vscode-extension/out/src/gitlab/gitlab_new_service.js:349:95)",
    "\tat Generator.throw (<anonymous>)",
    "\tat rejected (/Users/tomas/workspace/gitlab-vscode-extension/out/src/gitlab/gitlab_new_service.js:6:65)",
    "\tat processTicksAndRejections (internal/process/task_queues.js:93:5)"
  ]
}

How to review

This MR is a bit larger. The key to understanding this MR is to understand the createNewComment method: !266 (comment 589983226). The rest of the MR are tests and some helper functions.

Related to #342 (closed)