Add multiple generate for enum generate is, as, try_into

[A4-Tacks]

Close #11227

Examples

enum Variant {
    Undefined,
    $0Minor,
    M$0ajor,
}

->

enum Variant {
    Undefined,
    Minor,
    Major,
}

impl Variant {
    /// Returns `true` if the variant is [`Minor`].
    ///
    /// [`Minor`]: Variant::Minor
    #[must_use]
    fn is_minor(&self) -> bool {
        matches!(self, Self::Minor)
    }

    /// Returns `true` if the variant is [`Major`].
    ///
    /// [`Major`]: Variant::Major
    #[must_use]
    fn is_major(&self) -> bool {
        matches!(self, Self::Major)
    }
}

---

enum Value {
    Unit(()),
    $0Number(i32),
    Text(String)$0,
}

->

enum Value {
    Unit(()),
    Number(i32),
    Text(String),
}

impl Value {
    fn try_into_number(self) -> Result<i32, Self> {
        if let Self::Number(v) = self {
            Ok(v)
        } else {
            Err(self)
        }
    }

    fn try_into_text(self) -> Result<String, Self> {
        if let Self::Text(v) = self {
            Ok(v)
        } else {
            Err(self)
        }
    }
}

---

enum Value {
    Unit(()),
    $0Number(i32),
    Text(String)$0,
}

->

enum Value {
    Unit(()),
    Number(i32),
    Text(String),
}

impl Value {
    fn as_number(&self) -> Option<&i32> {
        if let Self::Number(v) = self {
            Some(v)
        } else {
            None
        }
    }

    fn as_text(&self) -> Option<&String> {
        if let Self::Text(v) = self {
            Some(v)
        } else {
            None
        }
    }
}