Since a lot of float methods are not included in core, I decided to make a simple polyfills crate, so we don't have to conditionally compile every place where these methods are used.

This adds a dependency, that does nothing if we use std. We can either:

1. Leave as it is, with additional dependency.
2. If we don't want to add a dependendy by default, we can introduce a std-polyfills (or no-std) feature flag (additional to std). I did something like that here: fix(no_std): final patches needed for no_std #1833.
   This has one drawback - we have to use either std or std-polyfills feature flag or the library won't compile.
   To make it easier on the user, we can add a check in lib.rs that emitts compiler error "either std or std-polyfills feature flag must be enabled" in such cases.
3. I can try to make the float-polyfills crate lighter, not depending on libm (or gate libm behind feature flag).

Let me know what you think and if you have some other ideas for this.

Related: rust-lang/rust#137578