Add ide-assist, generate single field struct From

[A4-Tacks]

Close rust-lang/rust-analyzer#19696

Assist: generate_single_field_struct_from

Implement From for a single field structure, ignore trivial types.

# //- minicore: from, phantom_data
use core::marker::PhantomData;
struct $0Foo<T> {
    id: i32,
    _phantom_data: PhantomData<T>,
}

->

use core::marker::PhantomData;
struct Foo<T> {
    id: i32,
    _phantom_data: PhantomData<T>,
}

impl<T> From<i32> for Foo<T> {
    fn from(id: i32) -> Self {
        Self { id, _phantom_data: PhantomData }
    }
}

[A4-Tacks]

r? @Veykril

[A4-Tacks]

@ShoyuVanilla Can merge this pr?

[ShoyuVanilla]

I forgot about this as I didn't have merge permission then 😅