SVG <text> does not use fallback fonts for missing glyphs

# SVG `<text>` does not use fallback fonts for missing glyphs

## Summary

Some characters are rendered as missing-glyph boxes when used inside SVG `<text>` with a generic font such as `serif`.

The same character renders correctly as normal HTML text. Explicitly selecting a font that contains the character also makes it render correctly inside SVG.

For example, the treble clef character `U+1D11E` does not render correctly in this SVG:

### Minimal example:

```html
<!doctype html>
<meta charset="utf-8">

<svg xmlns="http://www.w3.org/2000/svg" width="120" height="140">
  <text x="10" y="100" font-family="serif" font-size="86">
    &#x1D11E;
  </text>
</svg>
```

The same character renders correctly outside SVG:

```html
<!doctype html>
<meta charset="utf-8">

<span style="font-size: 86px; font-family: serif;">&#x1D11E;</span>
```

It also renders correctly inside SVG when the font is specified explicitly:

```html
<svg xmlns="http://www.w3.org/2000/svg" width="120" height="140">
  <text x="10" y="100" font-family="Noto Music" font-size="86">
    &#x1D11E;
  </text>
</svg>
```

I reproduced the same missing-glyph behaviour with several other symbols and characters when they require a fallback font.

## Steps to reproduce

1. Save the first HTML example to a file.
2. Open it in Ladybird.
3. The treble clef is displayed as a missing-glyph box.
4. Open the second example with the normal HTML `<span>`.
5. The treble clef is displayed correctly.
6. Change the SVG `font-family` from `serif` to `Noto Music`.
7. The treble clef is displayed correctly.

## Expected behaviour

SVG `<text>` should use an available fallback font when the selected font does not contain the requested character.

The treble clef should render correctly with `font-family="serif"` in the same way it does in normal HTML text.

## Build information 
System: Debian GNU/Linux 13 (trixie)
commit: bf6c4c71fd5b6ca76cbfbd92d759f0d3644fb0bd

## More examples:

### Different tests:
```html
<!doctype html>
<meta charset="utf-8">
<title>Ladybird SVG musical symbol fallback test</title>

<style>
  body { font-family: sans-serif; margin: 20px; }
  .test { margin-bottom: 24px; }
  .label { margin-bottom: 6px; font-weight: bold; }
  svg { display: block; width: 760px; height: 120px; border: 1px solid #ccc; }
  text { font-size: 68px; }
</style>

<div class="test">
  <div class="label">HTML reference — serif</div>
  <div style="font: 68px serif;">𝄞 𝄢 𝅝 𝅗𝅥 𝅘𝅥 𝅘𝅥𝅮 ♭ ♮ ♯ ♪ ♫</div>
</div>

<div class="test">
  <div class="label">SVG — no font specified</div>
  <svg xmlns="http://www.w3.org/2000/svg" viewBox="0 0 760 120"><text x="15" y="85">𝄞 𝄢 𝅝 𝅗𝅥 𝅘𝅥 𝅘𝅥𝅮 ♭ ♮ ♯ ♪ ♫</text></svg>
</div>

<div class="test">
  <div class="label">SVG — generic serif</div>
  <svg xmlns="http://www.w3.org/2000/svg" viewBox="0 0 760 120"><text x="15" y="85" font-family="serif">𝄞 𝄢 𝅝 𝅗𝅥 𝅘𝅥 𝅘𝅥𝅮 ♭ ♮ ♯ ♪ ♫</text></svg>
</div>

<div class="test">
  <div class="label">SVG — missing font, then serif fallback</div>
  <svg xmlns="http://www.w3.org/2000/svg" viewBox="0 0 760 120"><text x="15" y="85" font-family="'Definitely Missing Font', serif">𝄞 𝄢 𝅝 𝅗𝅥 𝅘𝅥 𝅘𝅥𝅮 ♭ ♮ ♯ ♪ ♫</text></svg>
</div>

<div class="test">
  <div class="label">SVG — missing font, then Noto Music fallback</div>
  <svg xmlns="http://www.w3.org/2000/svg" viewBox="0 0 760 120"><text x="15" y="85" font-family="'Definitely Missing Font', 'Noto Music', serif">𝄞 𝄢 𝅝 𝅗𝅥 𝅘𝅥 𝅘𝅥𝅮 ♭ ♮ ♯ ♪ ♫</text></svg>
</div>

<div class="test">
  <div class="label">SVG — explicit Noto Music</div>
  <svg xmlns="http://www.w3.org/2000/svg" viewBox="0 0 760 120"><text x="15" y="85" font-family="Noto Music">𝄞 𝄢 𝅝 𝅗𝅥 𝅘𝅥 𝅘𝅥𝅮 ♭ ♮ ♯ ♪ ♫</text></svg>
</div>
```

### Other symbols:
```html
<!doctype html>
<meta charset="utf-8">
<title>Ladybird SVG font fallback test</title>

<style>
  body { font-family: sans-serif; margin: 20px; }
  .test { margin-bottom: 22px; }
  .label { margin-bottom: 5px; font-weight: bold; }
  svg { display: block; width: 1100px; height: 100px; }
  text { font-size: 56px; }
</style>

<div class="test">
  <div class="label">HTML — generic serif</div>
  <div style="font: 56px serif;">∑ ∫ √ ∞ ≠ ♔ ♕ ✓ ★ ☀ Ω Ж ש م 中 𝔄 𝕭 𝟘 𐐀 𓀀 😀</div>
</div>

<div class="test">
  <div class="label">SVG — no font specified</div>
  <svg xmlns="http://www.w3.org/2000/svg" viewBox="0 0 1100 100"><text x="10" y="68">∑ ∫ √ ∞ ≠ ♔ ♕ ✓ ★ ☀ Ω Ж ש م 中 𝔄 𝕭 𝟘 𐐀 𓀀 😀</text></svg>
</div>

<div class="test">
  <div class="label">SVG — generic serif</div>
  <svg xmlns="http://www.w3.org/2000/svg" viewBox="0 0 1100 100"><text x="10" y="68" font-family="serif">∑ ∫ √ ∞ ≠ ♔ ♕ ✓ ★ ☀ Ω Ж ש م 中 𝔄 𝕭 𝟘 𐐀 𓀀 😀</text></svg>
</div>

<div class="test">
  <div class="label">SVG — missing font, then serif</div>
  <svg xmlns="http://www.w3.org/2000/svg" viewBox="0 0 1100 100"><text x="10" y="68" font-family="'Definitely Missing Font', serif">∑ ∫ √ ∞ ≠ ♔ ♕ ✓ ★ ☀ Ω Ж ש م 中 𝔄 𝕭 𝟘 𐐀 𓀀 😀</text></svg>
</div>

<div class="test">
  <div class="label">SVG — Noto Sans Symbols 2</div>
  <svg xmlns="http://www.w3.org/2000/svg" viewBox="0 0 1100 100"><text x="10" y="68" font-family="'Noto Sans Symbols 2', serif">∑ ∫ √ ∞ ≠ ♔ ♕ ✓ ★ ☀ Ω Ж ש م 中 𝔄 𝕭 𝟘 𐐀 𓀀 😀</text></svg>
</div>

<div class="test">
  <div class="label">SVG — Noto Sans Math</div>
  <svg xmlns="http://www.w3.org/2000/svg" viewBox="0 0 1100 100"><text x="10" y="68" font-family="'Noto Sans Math', serif">∑ ∫ √ ∞ ≠ ♔ ♕ ✓ ★ ☀ Ω Ж ש م 中 𝔄 𝕭 𝟘 𐐀 𓀀 😀</text></svg>
</div>

<div class="test">
  <div class="label">SVG — Noto Color Emoji</div>
  <svg xmlns="http://www.w3.org/2000/svg" viewBox="0 0 1100 100"><text x="10" y="68" font-family="'Noto Color Emoji', serif">☀ ★ ✓ 😀 😎 🚚 🎹 🦆</text></svg>
</div>
```

<img width="1920" height="1048" alt="Image" src="https://github.com/user-attachments/assets/8da9c861-9d9d-4ec6-a384-3e68d90dd211" />

<img width="1498" height="1047" alt="Image" src="https://github.com/user-attachments/assets/29e9bd60-a913-4b48-9034-fd29cedf09b2" />

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SVG <text> does not use fallback fonts for missing glyphs #11031

SVG `<text>` does not use fallback fonts for missing glyphs

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Uh oh!

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SVG <text> does not use fallback fonts for missing glyphs #11031

Description

SVG <text> does not use fallback fonts for missing glyphs

Summary

Minimal example:

Steps to reproduce

Expected behaviour

Build information

More examples:

Different tests:

Other symbols:

Metadata

Metadata

Assignees

Labels

Type

Projects

Milestone

Relationships

Development

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SVG `<text>` does not use fallback fonts for missing glyphs