UnderlineNav: Use anchoredPosition to position overflow menu

[siddharthkp]

• Fixes part of Underline nav: Should it have default paddings around? #4404

Instead of keeping the position fixed, adjust the position based on the space available (by using anchoredPosition)

Prefers aligning left towards the other link, but switches to right when there is not enough space:

underlinenav-anchored-overflow.mov

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Merge checklist

• Added/updated tests
• Added/updated documentation
• Added/updated previews (Storybook)
• Changes are SSR compatible
• Tested in Chrome
• Tested in Firefox
• Tested in Safari
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• (GitHub staff only) Integration tests pass at github/github (Learn more about how to run integration tests)

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🦋 Changeset detected

Latest commit: 6555591

The changes in this PR will be included in the next version bump.

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@primer/react	Patch

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[github-actions]

size-limit report 📦

Path	Size
packages/react/dist/browser.esm.js	87.41 KB (-0.03% 🔽)
packages/react/dist/browser.umd.js	87.79 KB (+0.05% 🔺)

[joshblack]

Closes #4059, I think, if that would be helpful to add to the PR description 👀

[broccolinisoup]

Hello @siddharthkp! I apologise not responding to the issue yesterday before you pushed this PR 😢

We already have an open PR #4234 to fix this and I gave feedback as well. I had issues with the CI jobs and didn't have a chance to get back to it so haven't merged that yet.

My main feedback was around when to use anchor positioning. If I am not underestimating the use cases, we don't actually need anchor positioning until we are short on space and that way, we don't have to calculate the menu position in every render when there is a resize.

Again sorry for that it is my bad that we ended up with two PRs for the same issue 😭 Would you be able to have a look at #4234 and share if you have any feedback?

[siddharthkp]

Closing as duplicate of #4234 🎉