Fix AnchorLinks last link not mark as active if target is at end of page

[juancwu]

Description

This PR fixes the issue where the last link is never marked as active if the target element is right at the end of the page. The abnormal behaviour was that the second to last link is always the one marked as active because the AnchorLinks component chooses the closest one to the top when multiple targets are in view.

Linked Issues

• Fixes [FE Bug] AnchorLinks does not set last link as active when last element is small in height #161

Testing

• Add new AnchorLinks component test components/test/AnchorLinks.test.tsx
• The test only test for the existence of the links but not able to test scroll since jsDom does not implement layouts.

Checklist

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Additionally, make sure that:

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• I have added tests that prove my fix is effective or that my feature works.
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[AmirAgassi]

lgtm