rustdoc generates broken link for inherent methods on primitive types on source code pages under `--generate-link-to-definition`

[fmease]

Reproducer 0:

fn scope() {
    let _ = 0usize.saturating_add(1);
}

On the source code page, saturating_add links to https://doc.rust-lang.org/nightly/core/foreigntype.num.html#method.saturating_add which is broken. It should link to https://doc.rust-lang.org/nightly/std/primitive.usize.html#method.saturating_add or https://doc.rust-lang.org/nightly/core/primitive.usize.html#method.saturating_add instead.

Reproducer 1:

fn scope() {
    let _ = false.then_some(());
}

On the source code page, then_some links to https://doc.rust-lang.org/nightly/core/foreigntype.bool.html#method.then_some which is broken. It should link to https://doc.rust-lang.org/nightly/std/primitive.bool.html#method.then_some or https://doc.rust-lang.org/nightly/core/primitive.bool.html#method.then_some instead.

[abdul2801]

@rustbot claim

[GuillaumeGomez]

@abdul2801 actually took #156706, so unassigned them.

Taking a look.

[GuillaumeGomez]

Opened #156736.