Update illustration sprite and previews

Purpose

• Add svg_size to a sprite json because illustrations have a fixed size in compare with icons.
• Add illustrations from a sprite to a previewer, so they can support dark mode.

⚠️ Excluding some old illustrations and logotypes from a sprite is intentional. They are still available, but not visible. Logotypes probably should be moved to a logos folder. And old illustrations will be removed.

Screenshots

before	after
CleanShot_2025-04-07_at_17.28.53	CleanShot_2025-04-07_at_17.28.23

Checklist

For a new icon and/or illustration:

• Link to related design issue:
• If this adds an icon ensure that it follows the new icon checklists.
• If this adds an illustration ensure that it follows the new illustration checklists.

For third-party trademarks:

• If this adds or updates an icon or illustration that includes a third-party trademark, ensure that it follows the process for adding third-party trademarks to GitLab.

gitlab#512693 (closed)