Move link icon to comment on a file line from HAML to CSS (repository)

What does this MR do?

When viewing large files via the blob viewer, an SVG image is generated for each line to display a link icon, this causes a significant bloat in file size.

This MR moves the link icon from haml to CSS.

Example of a large file: https://staging.gitlab.com/gpt/large_projects/gitlabhq1/blob/master/fixtures/emojis/index.json

Screenshots (strongly suggested)

Before (13.46MB)

After (7.29MB)

Does this MR meet the acceptance criteria?

Conformity

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Availability and Testing

• Review and add/update tests for this feature/bug. Consider all test levels. See the Test Planning Process.
• Tested in all supported browsers