Enhancement on the UI functions per source code line
### Description
At this moment, on Gitlab web UI for source code line, the only function provides the permalink which need to be expanded for more functions.
### Proposal
Enhanced menu for source code line similar to below.

### Links / references
Current UI.

### Documentation blurb
#### Overview
This is a popup menu when user clicks the number then the triple-dot. The menu could contain items for the operations against the current source code line, e.g. open a new issue for it with the permalink of it pre-filled in issue description.
#### Use cases
This is for better developer productivity. User could perform actions for the operations for the current line without switching to other views.
### Feature checklist
Make sure these are completed before closing the issue,
with a link to the relevant commit.
- [ ] [Feature assurance](https://about.gitlab.com/handbook/product/#feature-assurance)
- [ ] Documentation
- [ ] Added to [features.yml](https://gitlab.com/gitlab-com/www-gitlab-com/blob/master/data/features.yml)
issue