This was caused by converting the validation response to boolean instead
of returning all details.

docs: turn MR description into a list

See merge request gitlab-org/gitlab-vscode-extension!267

refactor: handle commenting on the last line

See merge request gitlab-org/gitlab-vscode-extension!271

refactor: fix diff algorithm

See merge request gitlab-org/gitlab-vscode-extension!268

chore: fix eslint errors that got to master from outdated MR

See merge request gitlab-org/gitlab-vscode-extension!269

fix: remove the broken code related to creating user snippets

See merge request gitlab-org/gitlab-vscode-extension!265

By stipping away all but unchanged lines we allowed edge cases when
a file started or ended with changes. In this scenario we wrongly
addded unchanged lines to the beginning or the end of the file.

feat: create new MR diff comments

See merge request gitlab-org/gitlab-vscode-extension!266

reafactor: prepare for creating new comments on MR diff

See merge request gitlab-org/gitlab-vscode-extension!263

test: make sure that integration test failure gets reported

See merge request gitlab-org/gitlab-vscode-extension!260

When we dispose commentController, all its therads will get disposed
automatically. We don't ever need to call dispose outside of the
GitLabCommentThread.

docs: make README more user oriented

See merge request gitlab-org/gitlab-vscode-extension!262

chore: enable no-floating-promises eslint rule

See merge request gitlab-org/gitlab-vscode-extension!264

We can use the standard `getActiveRepositoryOrSelectOne()` and delete
the custom project picker.

Also, we can remove the duplicated block for getting project to put the
snippet in.

Lastly, this commit converts several nested if statement into early
return statements.

Creating snippets in user space hasn't worked in a long time. And for
the last year, when the extension supports multiple GitLab instances, we
wouldn't know which instance to use for adding the user snippet.

This commit removes the broken logic and focuses on creating project
snippets.

create_snippet was the only client using the function

Most of the client code was making its own `assert()`, because it
couldn't continue without having an existing repository. By moving the
assert into the `getRepository()` method, we simplify the client code.

Multiple paces will need to search through all the MR changes and find
the correct diff. This commit extracts a method to do that.

When we create new diff threads, the API requires us to submit all three
values (start/base/head SHA) so even though we don't need startSha
internally, we have to parse it from the response.

refactor: track unchanged lines between new and old version of the diff

See merge request gitlab-org/gitlab-vscode-extension!261

refactor: create MR cache

See merge request gitlab-org/gitlab-vscode-extension!258

refactor: move diff line counting logic to separate module

See merge request gitlab-org/gitlab-vscode-extension!259

Added two new methods to the WrappedRepository: `reloadMr()` and
`getMr()`.

- `reloadMr()` will fetch additional information for the MR (for now
  it's the diff). It will also store this fetched information into a
  cache.
- `getMr()` expects that `reloadMr()` has been called in the past. It
  retrieves the MR information without making api calls.