Rollup merge of rust-lang#152512 - okaneco:exact_integer, r=tgross35

core: Implement feature `float_exact_integer_constants`

Accepted ACP - rust-lang/libs-team#713 (comment)
Tracking issue - rust-lang#152466

Implement accepted ACP for `MAX_EXACT_INTEGER` and `MIN_EXACT_INTEGER` on `f16`, `f32`, `f64`, and `f128`
Add tests to `coretests/tests/floats/mod.rs`

Author: Zalathar

src/codegen_f16_f128.rs

@@ -208,7 +208,7 @@ pub(crate) fn codegen_cast(
         let ret_ty = if to_ty.bits() < 32 { types::I32 } else { to_ty };
         let name = format!(
             "__fix{sign}tf{size}i",
-            sign = if from_signed { "" } else { "un" },
+            sign = if to_signed { "" } else { "uns" },
             size = match ret_ty {
                 types::I32 => 's',
                 types::I64 => 'd',