Rollup merge of rust-lang#144923 - rocurley:float_tests_refactor_3, r=tgross35

Move several more float tests to floats/mod.rs

This PR moves several tests to `floats/mod.rs`, as discussed in rust-lang#141726. The tests moved are:

* `test_abs`
* `test_signum`
* `test_is_sign_positive`
* `test_is_sign_negative`
* `test_next_up`
* `test_next_down`
* `test_sqrt_domain`
* `test_clamp_min_greater_than_max`
* `test_clamp_min_is_nan`
* `test_clamp_max_is_nan`
* `test_total_cmp`

This covers all the "easy" tests: the ones that don't have a lot of precision-specific constants. It's not clear to me that it's worth migrating the others.

Each test is its own commit (with the exception of the clamp tests), so it may be easiest to review each commit individually.

r? tgross35

Author: Zalathar