[Docs] Add link to Figma UI Kit

[elizabetdev]

Summary

Closes #3014.

This PR adds a link to the Figma UI Kit into the home page.

The Figma icon was optimized and resized to the same size as other third-parties icons. It was used as a custom SVG as mentioned on #3014.

Checklist

• Check against all themes for compatibility in both light and dark modes
• Checked in mobile
• Checked in IE11 and Firefox
• [ ] Props have proper autodocs
• [ ] Added documentation examples
• [ ] Added or updated jest tests
• [ ] Checked for breaking changes and labeled appropriately
• Checked for accessibility including keyboard-only and screenreader modes
• [ ] A changelog entry exists and is marked appropriately

[kibanamachine]

Preview documentation changes for this PR: https://eui.elastic.co/pr_3016/

[cchaos]

Nice! I like that you changed "Sketch" to just "Libraries". You might want to add a tooltip around the Figma one as well for those unfamiliar with the logo.

[kibanamachine]

Preview documentation changes for this PR: https://eui.elastic.co/pr_3016/

[cchaos]

😻 Thanks for adding this. Just had one extra comment for the old Sketch link

[snide]

Same comment as @cchaos. Thanks for adding this quick. Good to merge once changes are in.

[snide]

cc @hbharding so he's aware there will be a more prominent link.

[kibanamachine]

Preview documentation changes for this PR: https://eui.elastic.co/pr_3016/

[kibanamachine]

Preview documentation changes for this PR: https://eui.elastic.co/pr_3016/

[hbharding]

Thanks @miukimiu !