Rollup merge of #80720 - steffahn:prettify_prelude_imports, r=camelid,jyn514
Make documentation of which items the prelude exports more readable.
I recently figured out that rustdoc allows link inside of inline code blocks as long as they’re delimited with `<code> </code>` instead of `` ` ` ``. I think this applies nicely in the listing of prelude exports [in the docs](https://doc.rust-lang.org/std/prelude/index.html). There, currently unformatted `::` and `{ , }` is used in order to mimick import syntax while attatching links to individual identifiers.
## Rendered Comparison
### Currently (light)
![Screenshot_20210105_155801](https://user-images.githubusercontent.com/
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### After this PR (light)
![Screenshot_20210105_155811](https://user-images.githubusercontent.com/
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### Currently (dark)
![Screenshot_20210105_155824](https://user-images.githubusercontent.com/
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2a9f9e00-4f6f-11eb-95f9-
e291b5570b41.png)
### After this PR (dark)
![Screenshot_20210105_155836](https://user-images.githubusercontent.com/
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103661592-
2ffce880-4f6f-11eb-977a-
82afcb07d331.png)
### Currently (ayu)
![Screenshot_20210105_155917](https://user-images.githubusercontent.com/
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### After this PR (ayu)
![Screenshot_20210105_155923](https://user-images.githubusercontent.com/
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103661652-
3db26e00-4f6f-11eb-82b7-
378e38f0c41f.png)
_Edit:_ I just noticed, the “current” screenshots are from stable, so there are a few more differences in the pictures than the ones from just this PR.