Breadcrumbs jitter horizontally when switching symbols with emoji headings

Summary

Breadcrumb outline text shifts horizontally by a few pixels when the selected symbol changes (heading containing an emoji)

Description

Steps to reproduce:

1. Open a Markdown buffer with headings that contain emoji, e.g.:

   ## 🏗 Build
   - [ ] Generar el SDK de Yocto en CI/CD
   - [ ] Añadir el SDK de IMX9
   - [ ] Añadir el preset de IMX9
   
   ## 🔄 OSTree / OTA
   - [ ] az-updated: revisar edge cases en `docs/...`

2. Make sure breadcrumbs are enabled ("toolbar": { "breadcrumbs": true }).
3. Move the cursor between the sections so the symbol shown in the breadcrumb changes.

Expected behavior: The breadcrumb text stays in the same place, and only the symbol name changes.

Actual behavior: The outline/breadcrumb text moves a few pixels horizontally each time the symbol changes. This looks like a font metrics / glyph-advance mismatch. One candidate is the emoji glyph: 🏗 (U+1F3D7, text presentation by default, drawn monochrome) vs 🔄 (drawn in color), which probably come from different fallback fonts with different advances. Non-ASCII Latin text (ñ) is also present.

Screencast attached.

Zed Version and System Specs

Zed: v1.26.2+stable.384.c4273271092b0287f7d181f616bd5171e0a2f70c (Zed) OS: Linux Wayland ubuntu 26.04 Memory: 30.6 GiB Architecture: x86_64 GPU: Intel(R) UHD Graphics 630 (CFL GT2) || Intel open-source Mesa driver || Mesa 26.0.8-1ubuntu0.3

https://github.com/user-attachments/assets/27ca5304-647e-448b-87ea-cd6d79a1a04f