Make imap_go eval rule lazy in index argument (copy #2543)

[mergify]

Fixes #2542

The problem was that in the final recursive call, when imap_go would return Nil, the index argument was out-of-bounds. And because imap_go was strict in all arguments, imap_go would make the Nil undefined.

Subsequently applying reverse where the Nil is undefined, gives us a complete vector that is undefined, given that reverse is strict in its vector argument.

Still TODO:

• Write a changelog entry (see changelog/README.md)
• Check copyright notices are up to date in edited files

---

This is an automatic copy of pull request #2543 done by [Mergify](https://mergify.com).

[mergify]

Cherry-pick of a1dacb4 has failed:

On branch mergify/copy/1.8/pr-2543
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Unmerged paths:
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	both modified:   clash-ghc/src-ghc/Clash/GHC/Evaluator/Primitive.hs
	both modified:   tests/Main.hs

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[martijnbastiaan]

I'll fix the conflicts after merging #2946. I'll also add that PR on top.

[martijnbastiaan]

This has been backported already.