Add E2E coverage for using shortcut to open Web IDE from repo

Covers a happy path flow of using a keyboard shortcut to quickly open the Web IDE from any repo view. Negative and fringe scenarios will be covered with lower level specs.

To be completed together with gitlab-org/gitlab#340095 (closed)

Steps

1. Log into GitLab
2. Open a repository view in any project
3. Send keys: .
4. Verify Web IDE opens

This can easily be incorporated into existing E2E as most Web IDE tests are currently navigating to Web IDE via clicking the button on Project page - we will simply replace it by a shortcut in one of them without adding extra time cost.

Good candidate: qa/qa/specs/features/browser_ui/3_create/web_ide/link_to_line_in_web_ide_spec.rb