Stabilize const_float_classify

[eduardosm]

Tracking issue: #72505

Also reverts #114486

Closes #72505

Stabilized const API:

impl f32 {
    pub const fn is_nan(self) -> bool;
    pub const fn is_infinite(self) -> bool;
    pub const fn is_finite(self) -> bool;
    pub const fn is_subnormal(self) -> bool;
    pub const fn is_normal(self) -> bool;
    pub const fn classify(self) -> FpCategory;
    pub const fn is_sign_positive(self) -> bool;
    pub const fn is_sign_negative(self) -> bool;
}

impl f64 {
    pub const fn is_nan(self) -> bool;
    pub const fn is_infinite(self) -> bool;
    pub const fn is_finite(self) -> bool;
    pub const fn is_subnormal(self) -> bool;
    pub const fn is_normal(self) -> bool;
    pub const fn classify(self) -> FpCategory;
    pub const fn is_sign_positive(self) -> bool;
    pub const fn is_sign_negative(self) -> bool;
}

cc @rust-lang/wg-const-eval @rust-lang/libs-api

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[bors]

☔ The latest upstream changes (presumably #130253) made this pull request unmergeable. Please resolve the merge conflicts.

[thomcc]

I think libs-api needs to handle these?
r? libs-api

[RalfJung]

Cc @rust-lang/wg-const-eval -- this is entirely harmless, the methods just all use already-stable const facilities.

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