Fixed animation reset bug

[R-Cramer4]

An animation could be reset or not run if the dependencies of a binding are changed without actually changing the animation values. This is most notable on embedded hardware as you can force things to change at the frame rate therefore pausing the animation. On desktop it is noticeable as a jitter, and a reproducible example is:

AppWindow.slint

export struct Row { counter: int, active: bool }

export component AppWindow inherits Window {
    in property <[Row]> model;
    width: 300px;
    height: 100px;

    for row[i] in model : Rectangle {
        background: red;
        width: 50px;
        height: 50px;
        x: row.active ? 200px : 0px;
        animate x { duration: 3000ms; }
    }

    Text { text: model[0].counter; }
}

main.rs:

use slint::{Timer, TimerMode, VecModel, Model};
use std::rc::Rc;

slint::include_modules!();

fn main() {
    let app = AppWindow::new().unwrap();
    let rows = Rc::new(VecModel::from(vec![Row { counter: 0, active: false }]));
    app.set_model(rows.clone().into());

    // Spurious per-frame dirty: rewrites `counter` every ~16ms, `active` untouched.
    let timer = Timer::default();
    let rows_clone = rows.clone();
    timer.start(TimerMode::Repeated, std::time::Duration::from_millis(16), move || {
        let mut row = rows_clone.row_data(0).unwrap();
        row.counter += 1;
        rows_clone.set_row_data(0, row); // rewrites whole row -> marks dependents dirty every frame
    });

    // After 500ms, flip `active` once - this is the genuine change that should animate.
    let rows_clone2 = rows.clone();
    Timer::single_shot(std::time::Duration::from_millis(500), move || {
        let mut row = rows_clone2.row_data(0).unwrap();
        row.active = true;
        rows_clone2.set_row_data(0, row);
    });

    app.run().unwrap();
}

[tronical]

Looks generally good. This seems sensible behaviour.