Optimize layout of nested field-less enums

[newpavlov]

pub enum Bar {
    A = 1,
    B = 2,
    C = 3,
}

pub enum Baz {
    D = 4,
    E = 5,
    F = 6,
}

pub enum Foo {
    Bar(Bar),
    Baz(Baz),
}

Currently Foo takes 2 bytes, even though it can be trivially represented as a single u8.

[leoschwarz]

I think this is related to #46213, which is as far as I understand a more general case of your proposed optimization.

[newpavlov]

Hm, looks like it. I will close this issue in favor of the linked one.