Convert switch icon into icon font

What does this MR do?

Converts the switch icon into the exchange icon from font awesome

Are there points in the code the reviewer needs to double check?

Shouldn't be any

Why was this MR needed?

• Decreases an external resource for the repository compare page
• Icon font provides a sharper image for displays with higher pixel resolutions

What are the relevant issue numbers?

Closes #20508 (closed)

Screenshots (if relevant)

Before:

After:

Does this MR meet the acceptance criteria?

• CHANGELOG entry added
• Conform by the style guides
• Branch has no merge conflicts with master (if you do - rebase it please)
• Squashed related commits together