Implement trait Into<T> in lib-std

[ControlCplusControlV]

Sway should have an Into trait in the Standard library for

pub trait Into<T> {
    fn into(self) -> T;
}

Also From implementation should automatically derive Into

[mohammadfawaz]

This requires generic traits which we already have. It also requires trait constraints on impl blocks so that we can write:

// From implies Into
impl<T, U> Into<U> for T
where
    U: From<T>,
{
    /// Calls `U::from(self)`.
    ///
    /// That is, this conversion is whatever the implementation of
    /// `From<T>` for `U` chooses to do.
    fn into(self) -> U {
        U::from(self)
    }
}

where Into is defined as:

pub trait Into<T>: Sized {
    /// Converts this type into the (usually inferred) input type.
    fn into(self) -> T;
}

[nfurfaro]

@mohammadfawaz in light of #3637 , this issue could probably be simplified not to require any trait constraints, as we're moving towards decoupling From & Into.