settings ui: Add numeric steppers to settings UI (#39491)

This PR adds the numeric stepper component to the settings ui and
implements some settings that rely on this component as well.

I also switched {buffer/ui}_font_weight to the `gpui::FontWeight` type
and added a manual implementation of the Schemars trait. This allows Zed
to send min, max, and default information to the JSON LSP when a user is
manually editing the settings file.

The numeric stepper elements added to the settings ui are below:
- ui font size
- ui font weight
- Buffer font size
- Buffer font weight 
- Scroll sensitivity
- Fast scroll sensitivity
- Vertical scroll margin
- Horizontal scroll margin
- Inline blame padding 
- Inline blame delay
- Inline blame min column
- Unnecessary code fade
- Tab Size
- Hover popover delay

Release Notes:

- N/A

assets/settings/default.json

@@ -1231,6 +1231,10 @@
     // 2. Hide the gutter
     //      "git_gutter": "hide"
     "git_gutter": "tracked_files",
+    /// Sets the debounce threshold (in milliseconds) after which changes are reflected in the git gutter.
+    ///
+    /// Default: null
+    "gutter_debounce": null,
     // Control whether the git blame information is shown inline,
     // in the currently focused line.
     "inline_blame": {