Make std/src/num mirror core/src/num

[tgross35]

The float modules in std are currently top-level but for core, they are nested within the num directory and referenced by #[path = ...]. For consistency, adjust std to use the same structure as core.

Also change the f16 and f128 gates from outer attributes to inner attributes like core has.

[rustbot]

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[bors]

☔ The latest upstream changes (presumably #138768) made this pull request unmergeable. Please resolve the merge conflicts.

[workingjubilee]

??? why didn't I see this in my queue on previous checks?

[workingjubilee]

oh wait, I see, I remember...

...uh, can we just pub use $path in appropriate locations?

I think I withheld comment because I was going to take a closer look to validate whether that was doable before I left the review comment, but that was an inappropriate delay and I should have left the comment, then doublechecked if I had spare energy. Sorry.

[tgross35]

...uh, can we just pub use $path in appropriate locations?

Wondered about this too, I think it is because std::num is public so std::num::f32 and similar would also be public to reexport and we don't want that. It would be possible to move these into a new nonpublic {core, std}::float, but 🤷 since it's mostly for file organization. I have no preference here, so your call.

@rustbot ready

[bors]

☔ The latest upstream changes (presumably #139734) made this pull request unmergeable. Please resolve the merge conflicts.