Dequarantine old Web IDE tests

What does this MR do?

Dequarantines old Web IDE tests. The new Web IDE is currently in Beta and only enabled for users in gitlab.com, this means that all non-live environments and self-managed instances still use the old Web IDE by default. We should maintain some coverage till the feature is officially release and enabled by default, at that point the tests can be retired. Since the original reason for quarantining was feature flag flakiness, we will limit these runs to non-live environments where ff toggling is not required. Part of gitlab-org/quality/quality-engineering/team-tasks#1621 (closed).

NB: Web IDE now opens in a separate tab so "open in Web IDE" methods had to be slightly adjusted for the tests to continue working.

Also removes browser_ui/3_create/web_ide/open_fork_in_web_ide_spec.rb that is permanently skipped and is not bringing any value (see #351696 (closed)).

E2E Test Failure issue(s)

#387998 (closed)

Check-list

• General code guidelines check-list
  • Code review guidelines
  • Style guides
• Quarantine test check-list
  • Follow the Quarantining Tests guide.
  • Confirm the test has a quarantine: tag with the specified quarantine type.
  • Note if the test should be quarantined for a specific environment.
  • (Optionally) In case of an emergency (e.g. blocked deployments), consider adding labels to pick into auto-deploy (Pick into auto-deploy priority1 severity1).
• Dequarantine test check-list
  • Follow the Dequarantining Tests guide.
  • Confirm the test consistently passes on the target GitLab environment(s).
• To ensure a faster turnaround, ask in the #quality_maintainers Slack channel for someone to review and merge the merge request, rather than assigning it directly.