rustdoc rendered `const`s should respect `#[doc(hidden)]` fields

[SergioBenitez]

For a struct and const declared as:

pub struct HiddenFoo {
    #[doc(hidden)]
    pub foo: usize,
}

pub const SOME_FOO: HiddenFoo = HiddenFoo { foo: 10 };

rustdoc currently renders:

pub const SOME_FOO: HiddenFoo

SOME_FOO: HiddenFoo = HiddenFoo { foo: 10 };

This unhides the hidden foo field. Instead, it should respect the #[doc(hidden)] attribute on foo and render the following:

pub const SOME_FOO: HiddenFoo

SOME_FOO: HiddenFoo = HiddenFoo { .. };

Or, better yet, if all fields are hidden, then I'd prefer for it to not render the definition at all:

pub const SOME_FOO: HiddenFoo

[GuillaumeGomez]

Seems complicated since at the point we print it, we don't have fields declaration attributes anymore...

[ollie27]

Fixed by #53409. We don't show the values of consts anymore.