Rollup merge of #141521 - ruancomelli:const-float-rounding, r=RalfJung

Add `const` support for float rounding methods

# Add `const` support for float rounding methods

This PR makes the following float rounding methods `const`:

- `f64::{floor, ceil, trunc, round, round_ties_even}`
- and the corresponding methods for `f16`, `f32` and `f128`

Tracking issue: rust-lang/rust#141555

## Procedure

I followed rust-lang/rust@c09ed3e as closely as I could in making float methods `const`, and also received great guidance from https://internals.rust-lang.org/t/const-rounding-methods-in-float-types/22957/3?u=ruancomelli.

## Note

This is my first code contribution to the Rust project, so please let me know if I missed anything - I'd be more than happy to revise and learn more. Thank you for taking the time to review it!

Author: jhpratt

src/intrinsics/mod.rs

@@ -159,67 +159,6 @@ pub trait EvalContextExt<'tcx>: crate::MiriInterpCxExt<'tcx> {
                 this.write_scalar(Scalar::from_bool(branch), dest)?;
             }
 
-            "floorf16" | "ceilf16" | "truncf16" | "roundf16" | "round_ties_even_f16" => {
-                let [f] = check_intrinsic_arg_count(args)?;
-                let f = this.read_scalar(f)?.to_f16()?;
-                let mode = match intrinsic_name {
-                    "floorf16" => Round::TowardNegative,
-                    "ceilf16" => Round::TowardPositive,
-                    "truncf16" => Round::TowardZero,
-                    "roundf16" => Round::NearestTiesToAway,
-                    "round_ties_even_f16" => Round::NearestTiesToEven,
-                    _ => bug!(),
-                };
-                let res = f.round_to_integral(mode).value;
-                let res = this.adjust_nan(res, &[f]);
-                this.write_scalar(res, dest)?;
-            }
-            "floorf32" | "ceilf32" | "truncf32" | "roundf32" | "round_ties_even_f32" => {
-                let [f] = check_intrinsic_arg_count(args)?;
-                let f = this.read_scalar(f)?.to_f32()?;
-                let mode = match intrinsic_name {
-                    "floorf32" => Round::TowardNegative,
-                    "ceilf32" => Round::TowardPositive,
-                    "truncf32" => Round::TowardZero,
-                    "roundf32" => Round::NearestTiesToAway,
-                    "round_ties_even_f32" => Round::NearestTiesToEven,
-                    _ => bug!(),
-                };
-                let res = f.round_to_integral(mode).value;
-                let res = this.adjust_nan(res, &[f]);
-                this.write_scalar(res, dest)?;
-            }
-            "floorf64" | "ceilf64" | "truncf64" | "roundf64" | "round_ties_even_f64" => {
-                let [f] = check_intrinsic_arg_count(args)?;
-                let f = this.read_scalar(f)?.to_f64()?;
-                let mode = match intrinsic_name {
-                    "floorf64" => Round::TowardNegative,
-                    "ceilf64" => Round::TowardPositive,
-                    "truncf64" => Round::TowardZero,
-                    "roundf64" => Round::NearestTiesToAway,
-                    "round_ties_even_f64" => Round::NearestTiesToEven,
-                    _ => bug!(),
-                };
-                let res = f.round_to_integral(mode).value;
-                let res = this.adjust_nan(res, &[f]);
-                this.write_scalar(res, dest)?;
-            }
-            "floorf128" | "ceilf128" | "truncf128" | "roundf128" | "round_ties_even_f128" => {
-                let [f] = check_intrinsic_arg_count(args)?;
-                let f = this.read_scalar(f)?.to_f128()?;
-                let mode = match intrinsic_name {
-                    "floorf128" => Round::TowardNegative,
-                    "ceilf128" => Round::TowardPositive,
-                    "truncf128" => Round::TowardZero,
-                    "roundf128" => Round::NearestTiesToAway,
-                    "round_ties_even_f128" => Round::NearestTiesToEven,
-                    _ => bug!(),
-                };
-                let res = f.round_to_integral(mode).value;
-                let res = this.adjust_nan(res, &[f]);
-                this.write_scalar(res, dest)?;
-            }
-
             "sqrtf32" => {
                 let [f] = check_intrinsic_arg_count(args)?;
                 let f = this.read_scalar(f)?.to_f32()?;