feat: respond to an MR diff thread

See merge request gitlab-org/gitlab-vscode-extension!222

feat(mr review): show change type for each changed file

See merge request gitlab-org/gitlab-vscode-extension!213

fix(instanceurl): subpath in self-managed GitLab is not used #319

See merge request gitlab-org/gitlab-vscode-extension!206

fix: elliptic and y18n have vulnerabilities

See merge request gitlab-org/gitlab-vscode-extension!214

feat: rename 'Description' to 'Overview' in MR items

See merge request gitlab-org/gitlab-vscode-extension!219

docs: improve development process wording

See merge request gitlab-org/gitlab-vscode-extension!216

chore: update changelog to include CVE-2020-13279

See merge request gitlab-org/gitlab-vscode-extension!212

feat(sidebar): show welcome view if there are no tokens set

See merge request gitlab-org/gitlab-vscode-extension!205

refactor: prepare the code for thread replies

See merge request gitlab-org/gitlab-vscode-extension!208

Fix typo in step 3

See merge request gitlab-org/gitlab-vscode-extension!209

chore: remove VS Code settings that are not needed

See merge request gitlab-org/gitlab-vscode-extension!210

test: fail early when the test environment isn't correctly set up

See merge request gitlab-org/gitlab-vscode-extension!211

docs: update the security release process after 3.15.1 release

See merge request gitlab-org/gitlab-vscode-extension!207

If the integration test workspace is missing, fail the test instantly.
This improves contributor experience preventing
unrelated integration test failures.
This commit also moves the documentation for running integration tests
to a more prominent position in the docs.

- eslint setting is deprecated
- instanceUrl setting is not needed thanks to our heuristic for
guessing the instanceUrl from git remote

This is to be reverted in the next MR. This disabling is used instead of
a feature flag. Now the preliminary refactoring can be reviewed
separately.

We crated a fragment that contains all note information. We then use
this fragment for fetching discussions and for returning note from the
createNote mutation. We also had to fix the webview integration test
where the fake API response must now contain the note.

The real reason for this simplification is summed up in the following
line:

```
export type GqlNote = GqlTextDiffNote | GqlImageNote | GqlOverviewNote;
```

We can now refer to notes by GqlNote instead of having to specify
generic arguments. That makes the code easier to read and it will allow
us to return GqlNote from the createNote mutation.

Excluding the position from overview notes was a small optimization.
Removing the condition simplifies the code at the cost of small
overhead (currently roughly 20 requests per hour).
After this change we'll always fetch the diff position.

Backport security release 3.15.1 back to main branch

See merge request gitlab-org/security/gitlab-vscode-extension!8

fix: use the same git binary as VS Code

See merge request gitlab-org/security/gitlab-vscode-extension!7

refactor: refactor fetchIssuables to use URLSearchParams

See merge request gitlab-org/gitlab-vscode-extension!201

docs: remove branch rename notice

See merge request gitlab-org/gitlab-vscode-extension!204