Rotation-aware text layout

## What problem does this solve or what need does it fill?

Bevy UI can only draw text horizontally except if you apply rotation to the `TextBundle` entities transform which breaks the layout.

## What solution would you like?

Maybe add a `TextWritingMode` enum (The relevant property in CSS is called writing-mode) with `Horizontal` and `Vertical` variants initially. This isn't a feature that would make sense for `Text2dBundle`, so it shouldn't be a field that is added to the `Text` struct (unless we split up `Text` into `Text` and `Text2d` types, which might make sense as their behaviour is very different now).

The `Horizontal` variant would be what we have now, and the `Vertical` variant would match the behaviour of `writing-mode: vertical-rl` in CSS (example: [https://www.w3docs.com/tools/editor/9992](https://www.w3docs.com/tools/editor/9992)).

The implementation shouldn't be too tricky. It might be a little challenging if you aren't familiar with the bevy ui internals but still doable.

For rendering, in `extract_text_uinodes` if `TextWritingMode::Vertical` is set the transform needs to be rotated by `Quat::from_rotation_z(std::f32::consts::FRAC_PI_2)`. The translation might need adjustment too.

`measure_text_system` and `text_system` would also need changes and you'd need a new measure func. It should be enough I think to just wrap the existing `TextMeasure` in a new `Measure` type and swap the width and height:

```rust
pub struct VerticalTextMeasure {
pub text_measure: TextMeasure,
}

impl Measure for VerticalTextMeasure {
fn measure(
&self,
width: Option,
height: Option,
available_width: AvailableSpace,
_available_height: AvailableSpace,
) -> Vec2 {
self.text_measure.measure(height, width, available_height, available_width)
}
}
```

## Additional context

https://developer.mozilla.org/en-US/docs/Web/CSS/text-orientation
https://developer.mozilla.org/en-US/docs/Web/CSS/writing-mode
https://www.w3docs.com/learn-css/writing-mode.html

Start by reading the UI text paths named in the issue: extract_text_uinodes, measure_text_system, and text_system, along with TextMeasure and the Measure trait. Trace how horizontal text is measured, laid out, and transformed, then verify vertical writing-mode behavior with a UI example or relevant tests. Done means vertical UI text lays out and renders without relying on Text2dBundle rotation that breaks layout.

Written by the indexing model from the issue text.