`cosmic_text` font fallback causes inconsistent text rendering results

## Bevy version

Bevy: Latest `main`
Cargo: `cargo 1.82.0 (8f40fc59f 2024-08-21)`
OS: Windows 11

```ignore
`AdapterInfo { name: "NVIDIA GeForce RTX 4090", vendor: 4318, device: 9860, device_type: DiscreteGpu, driver: "NVIDIA", driver_info: "566.03", backend: Vulkan }`
```

## What you did

I discovered this issue while working on an i18n crate for Bevy that loads dynamic fonts based on the selected locale.

I put together a minimal reproduction repo here:
https://github.com/TurtIeSocks/bevy_font_bug

## What went wrong

While working on this crate I noticed that if a font wasn't using the dynamic font component, it was still able to successfully render characters from the fonts that I had used in other text components, even though the component in question was only using the default font included with Bevy. After putting together the minimal reproduction repo and taking a closer look at the debug logs, it seems that `cosmic_text` is caching fonts to use as a fallback when the given font does not have support for the necessary characters.

### Expectation

Texts should (?) render with the font that is (or isn't) provided,

### What Happened

Texts are automatically selecting previously used fonts as fallbacks.

## Additional information

These logs are taken from the minimal reproduction repo linked above:

### Logs from first render (when the font was not cached)

```
2024-11-11T17:18:24.216542Z DEBUG cosmic_text::font::fallback: failed to find family 'Segoe UI'
2024-11-11T17:18:24.216621Z DEBUG cosmic_text::font::fallback: failed to find family 'Segoe UI Emoji'
2024-11-11T17:18:24.218546Z DEBUG cosmic_text::font::fallback: failed to find family 'Segoe UI'
2024-11-11T17:18:24.218683Z DEBUG cosmic_text::font::fallback: failed to find family 'Segoe UI Emoji'
2024-11-11T17:18:24.218804Z DEBUG cosmic_text::font::fallback: failed to find family 'Segoe UI Symbol'
2024-11-11T17:18:24.218902Z DEBUG cosmic_text::font::fallback: failed to find family 'Segoe UI Historic'
2024-11-11T17:18:24.219010Z DEBUG cosmic_text::font::fallback: Failed to find any fallback for [Han] locale 'en-US': '界'
```

### Logs from the second render
```
2024-11-11T17:18:25.221886Z DEBUG cosmic_text::font::fallback: failed to find family 'Segoe UI'
2024-11-11T17:18:25.221966Z DEBUG cosmic_text::font::fallback: failed to find family 'Segoe UI Emoji'
2024-11-11T17:18:25.222059Z DEBUG cosmic_text::font::fallback: failed to find family 'Segoe UI Symbol'
2024-11-11T17:18:25.222179Z DEBUG cosmic_text::font::fallback: failed to find family 'Segoe UI Historic'
2024-11-11T17:18:25.222333Z DEBUG cosmic_text::font::fallback: Failed to find preset fallback for [Han] locale 'en-US', used 'Noto Sans JP': '界'
```

## Thoughts

I like the idea of having font fallbacks, especially for i18n purposes, but I think the undocumented behavior may just lead to confusion more than anything else. And as the logs mentioned, it says "Failed to find preset fallback", so I assume we can customize this in some way, which could be a desirable public API that could be added.

Couple of thoughts on this:
- Consider either disabling the fallback or expose the ability to customize it so users can set it
- If the latter, it should definitely be documented
- Less related but perhaps it would be beneficial if Bevy transitioned to using NotoSans and loads more variations of the fonts when the `default_font` feature is enabled - this way Bevy has international font support out of the box!