Rollup merge of #142243 - RalfJung:float-test-dedup, r=tgross35

float tests: deduplicate min, max, and rounding tests

Part of rust-lang/rust#141726

Best reviewed commit-by-commit.

- Use `assert_biteq!` in the `mod.rs` tests. This requires some trickery to make shadowing macros with imports work.
- The min, max, minimum, maximum tests in `tests/floats/f*.rs` are entirely subsumed by what we already have in `tests/float/mod.rs`, so I just removed them.
- The rounding tests (floor etc) in `f*.rs` had more test points, so I copied them over. They didn't have `0.5` and `-0.5` though which seem like interesting points in particular regarding the sign of the resulting zero if that's what it sounds to, and they didn't max min/max/inf/nan tests, so this was really a merger of both tests.

r? ``@tgross35``

Author: matthiaskrgr