New lint: `derived_partial_eq_with_manual_eq`

What it does

Disallows a type from having a derived PartialEq with a manual Eq implementation.

Advantage

• Prevents accidental wrong Eq implementations for types containing floats (for instance: https://github.com/mongodb/bson-rust/issues/683)

Drawbacks

No response

Example

#[derive(PartialEq)]
struct Foo {
    value: u32,
}

impl Eq for Foo {}

#[derive(PartialEq)]
struct Bar {
    value: f32,
}

impl Eq for Bar {}

Either both PartialEq and Eq should be manually implemented or both should be derived:

#[derive(PartialEq, Eq)]
struct Foo {
    value: u32,
}

struct Bar {
    value: f32,
}

impl PartialEq for Bar {
    fn eq(&self, other: &Self) -> bool {
        return self.value.to_bits() == other.value.to_bits()
    }
}

impl Eq for Bar {}

Note that the following doesn't compile:

#[derive(PartialEq, Eq)]
struct Bar {
    value: f32,
}

Comparison with existing lints

No response

Additional Context

No response