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

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.

This commit changes the way WrappedRepository exposes the
GitLabNewService. We used getter which was very hard to mock in tests.
Instead, we now use regular function (getGitLabService()) which is
easily replaced in tests.

Additionally, this commit creates a helper function for creating
WrappedRepository, because it is going to be used in many tests in the
future.

This commit replaces the GitLabRepository(GitLabWorkspace) interface
with the Wrapped repository. The original objects `{ label, uri, error}`
were constructed by the issuable.ts.

We now use the WrappedRepository and the error state is signaled by a
new `containsGitLabProject` boolean flag. I.e. if the wrapped repository
doesn't contain GitLab project, there has been error during fetching it.

Also having access to the wrapped repository from within mr_item_model
is going to be important in the next commit because it allows us to
interact with the MR cache.

This method isn't used outside of the wrapped_repository module.

fix: generating file link on windows uses backslash

See merge request gitlab-org/gitlab-vscode-extension!257

refactor: remove GitService in favour of WrappedRepository

See merge request gitlab-org/gitlab-vscode-extension!253

refactor: move project cache to WrappedRepository

See merge request gitlab-org/gitlab-vscode-extension!255

docs: improvements to self-signed certificates docs

See merge request gitlab-org/gitlab-vscode-extension!254

chore: establish CODEOWNERS for documentation

See merge request gitlab-org/gitlab-vscode-extension!256

refactor: move git related logic to the WrappedRepository

See merge request gitlab-org/gitlab-vscode-extension!250

chore: running npm audit fix to update vulnerable dependencies

See merge request gitlab-org/gitlab-vscode-extension!251

We will move much of the git code to synchronous execution. When the
git_extension_wrapper receives a new repository, the repository is most
likely not initialized yet. We can wait for the initialization with
repository.status().

refactor: expose GitService and GitLab service in WrappedRepository

See merge request gitlab-org/gitlab-vscode-extension!249

Extract GraphQL queries into separate files

See merge request gitlab-org/gitlab-vscode-extension!248