Macro impl_into_maybe_dyn_with_convert

macro_rules! impl_into_maybe_dyn_with_convert {
    ($ty:ty; $convert:expr $(; $($from:ty),*)?) => { ... };
}

Create From<U> implementations for MaybeDyn<T> for a list of types.

Usually, you would use the impl_into_maybe_dyn! macro instead of this macro.