Auto merge of #138062 - LorrensP-2158466:miri-enable-float-nondet, r=RalfJung

Enable Non-determinism of float operations in Miri and change std tests

Links to [#4208](rust-lang/miri#4208) and [#3555](rust-lang/miri#3555) in Miri.

Non-determinism of floating point operations was disabled in rust-lang/rust#137594 because it breaks the tests and doc-tests in core/coretests and std. This PR enables some of them.

This pr includes the following changes:

- Enables the float non-determinism but with a lower relative error of 4ULP instead of 16ULP
- These operations now have a fixed output based on the C23 standard, except the pow operations, this is tracked in [#4286](rust-lang/miri#4286 (comment))
- Changes tests that made incorrect assumptions about the operations, not to make that assumption anymore (from `assert_eq!` to `assert_approx_eq!`.
- Changed the doctests of the stdlib of these operations to compare against fixed constants instead of `f*::EPSILON`, which now succeed with Miri and `-Zmiri-many-seeds`
- Added a constant `APPROX_DELTA` in `std/tests/floats/f32.rs` which is used for approximation tests, but with a different value when run in Miri. This is to make these tests succeed.
- Added tests in the float tests of Miri to test the C23 behaviour.

Fixes rust-lang/miri#4208

Author: bors