Rollup merge of #50588 - ExpHP:i-can-see-my-house-from-here, r=frewsxcv

Move "See also" disambiguation links for primitive types to top

Closes #50384.

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<summary>Images</summary>

![rust-slice](https://user-images.githubusercontent.com/1411280/39843148-caa41c3e-53b7-11e8-8123-b57c25a4d9e0.png)

![rust-isize](https://user-images.githubusercontent.com/1411280/39843146-ca94b384-53b7-11e8-85f3-3f5e5d353a05.png)

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r? @steveklabnik

diff --cc src/libstd/f32.rs
Simple merge

diff --cc src/libstd/f64.rs
Simple merge