project_panel: Add bold_folder_labels setting (#47631)

This setting brings Zed in parity with Sublime's `bold_folder_labels`.

The settings does just that, it makes directory labels bold. This
setting is
particularly useful for those who turn icons off, but do need a visual
queue (besides the chevron) to quickly tell apart files and folders.

Note: This PR depends on
https://github.com/zed-industries/zed/pull/47629.
Otherwise, the setting will appear to have no uneffect (unless you're
using a custom UI font). ZedSans has "bold" today, but that's too thick
for the project panel.

<img width="2282" height="1545" alt="zed-project-panel"
src="https://github.com/user-attachments/assets/63ccacc0-c00a-48b2-8e70-923aa6717956"
/>

Release Notes:

- Added `project_panel.bold_folder_labels` to show folder names with
bold text in the project panel (defaults to `false`).

docs/src/visual-customization.md

@@ -453,6 +453,7 @@ Project panel can be shown/hidden with {#action project_panel::ToggleFocus} ({#k
     "indent_size": 20,              // Pixels for each successive indent
     "auto_reveal_entries": true,    // Show file in panel when activating its buffer
     "auto_fold_dirs": true,         // Fold dirs with single subdir
+    "bold_folder_labels": false,    // Show folder names with bold text
     "sticky_scroll": true,          // Stick parent directories at top of the project panel.
     "drag_and_drop": true,          // Whether drag and drop is enabled
     "scrollbar": {                  // Project panel scrollbar settings