Rollup merge of #66837 - ohadravid:epsilon-doc, r=dtolnay

Rollup merge of #66837 - ohadravid:epsilon-doc, r=dtolnay

Clarify `{f32,f64}::EPSILON` docs

The doc for `EPSILON` says:
>  This is the difference between `1.0` and the next **largest** representable number.

Which is a bit unclear.

[Wikipedia](https://en.wikipedia.org/wiki/Machine_epsilon) says
> Machine epsilon is defined as the difference between 1 and the next **larger** floating point number

So this PR update the docs to match the Wikipedia version.

The original PR also has this in a [comment](https://github.com/rust-lang/rust/pull/50919#discussion_r192600209).