`UiTransform.scale` breaks text rendering, image scaling and border radius

## Bevy 0.18

## What you did

Add a `Node` with overflow set to `scroll` and a (larger) child `Node` which is then scaled using `UiTransform`.

## What went wrong

- A `ImageNode` with `ImageNodeMode::Stretch` on the child does not scale correctly. Setting scale to 3 for example, appears to scale down the node.
- `Text` or `TextSpan` components on the child (or its descendants) stretch the text when close to the border of the parent.
- The borders of the descendants of the child scale incorrectly and seem to grow disproportionally fast when the descendant is (partially) outside the bounds of the parent.

https://github.com/user-attachments/assets/6fa38aee-a68d-4d71-a128-5c9c9adfac9d

## Additional information

The code to produce the above app

```rust

use bevy::{
asset::RenderAssetUsages, ecs::relationship::{RelatedSpawnerCommands, Relationship}, prelude::*, render::render_resource::{Extent3d, TextureDimension, TextureFormat}
};
fn main() {
App::new()
.add_plugins((DefaultPlugins,))
.add_systems(Startup, setup)
.add_systems(Update, update_scale)
.run();
}

#[derive(Component)]
struct ScaleText;
#[derive(Component)]
struct Scale;

fn update_scale(
mut scaled_background: Single<&mut UiTransform, With>,
mut text: Single<&mut TextSpan, With>,
time: Res,
) {
let scale = (time.elapsed_secs() * 0.4).cos() * (1.95) + 2.05; // 0.1 .. 4
scaled_background.scale = Vec2::splat(scale);
text.0 = format!("{scale:.2}");
}

fn setup(mut commands: Commands, mut images: ResMut>) {
commands.spawn(Camera2d);

commands
.spawn(Node {
display: Display::Grid,
width: vw(100),
height: vh(100),
padding: UiRect::all(px(20)),
column_gap: px(20),
row_gap: px(20),
grid_template_columns: vec![RepeatedGridTrack::fr(2, 1.0)],
grid_template_rows: vec![RepeatedGridTrack::auto(1), RepeatedGridTrack::fr(1, 1.0)],
..Default::default()
})
.with_children(|parent| {
parent.spawn((
Node {
grid_column: GridPlacement::span(2),
..Default::default()
},
Text("The left and right panel contain the same content. The left panels content is scaled with a scale factor of ".into()),
)).with_children(|text| {
text.spawn((TextSpan("-/-".into()), TextColor(Srgba::RED.into()), ScaleText));
text.spawn(TextSpan(" whereas the right panel is not scaled (scale = 1).".into()));
});

let background = images.add(uv_debug_texture());
spawn_content(parent, background.clone(), true);
spawn_content(parent, background, false);
});
}

fn spawn_content(commands: &mut RelatedSpawnerCommands, background: Handle, with_scale: bool) {
const BACKGROUND_SIZE: f32 = 40960.0;
commands.spawn((
Node {
border: UiRect::all(px(2)),
overflow: Overflow::scroll(),
..Default::default()
},
ScrollPosition(Vec2::splat(BACKGROUND_SIZE / 2.0)),
BorderColor::all(Color::WHITE),
)).with_children(|parent| {
parent.spawn((
Node {
min_width: px(BACKGROUND_SIZE),
min_height: px(BACKGROUND_SIZE),
..Default::default()
},
BackgroundColor(Srgba::BLUE.into()),
ImageNode::new(background).with_mode(NodeImageMode::Stretch),
)).insert_if(Scale, || with_scale)
.with_child((
Node {
position_type: PositionType::Absolute,
width: px(300),
height: px(300),
border: UiRect::all(px(2)),
border_radius: BorderRadius::all(px(30)),
..Default::default()
},
UiTransform::from_translation(Val2::px(BACKGROUND_SIZE / 2.0, BACKGROUND_SIZE / 2.0)),
BackgroundColor(Color::BLACK.with_alpha(0.75)),
BorderColor::all(Color::WHITE),
children![(
Text("Hello World!".into()),
Node {
margin: UiRect::all(Val::Auto),
..Default::default()
}
)]
));
});
}

/// Creates a colorful test pattern
fn uv_debug_texture() -> Image {
const TEXTURE_SIZE: usize = 256;

let mut texture_data = [0; TEXTURE_SIZE * TEXTURE_SIZE * 4];
for y in 0..TEXTURE_SIZE {
for x in 0.. TEXTURE_SIZE {
let index = 4 * (y * TEXTURE_SIZE + x);
let color = if (x + y) % 2 == 0 {
[0, 0, 0, 255]
} else {
[255 * (x % 2) as u8, 255 * (y % 2) as u8, 0, 255]
};
texture_data[index..index + 4].copy_from_slice(&color);
}
}

let mut img = Image::new_fill(
Extent3d {
width: TEXTURE_SIZE as u32,
height: TEXTURE_SIZE as u32,
depth_or_array_layers: 1,
},
TextureDimension::D2,
&texture_data,
TextureFormat::Rgba8UnormSrgb,
RenderAssetUsages::RENDER_WORLD,
);
img.sampler = bevy::image::ImageSampler::nearest();
img
}

```

Start by running the supplied Rust reproduction and observe the scaled and unscaled panels side by side. Trace the interaction between UiTransform, overflow scrolling, ImageNodeMode::Stretch, Text/TextSpan, borders, and border_radius; done means image scaling, text layout, and descendant borders remain correct at varying scale values.

Written by the indexing model from the issue text.