settings_ui: Correct stepper increment and enforce max value for Centered Layout Padding (#40751)

Closes #40748

This PR improves the Centered Layout Padding in settings ui by limiting the numeric stepper to be within valid values and adding a custom schema generated to improve the JSON LSP completions and warnings when editing the setting field manually.

Release Notes:

- settings ui: limit stepper increment for centered padding between 0 and 0.4 and increment by 0.05 now

---------

Co-authored by: Anthony Eid <anthony@zed.dev>

crates/ui_input/src/number_field.rs

@@ -8,7 +8,7 @@ use std::{
 use editor::{Editor, EditorStyle};
 use gpui::{ClickEvent, Entity, FocusHandle, Focusable, FontWeight, Modifiers};
 
-use settings::{CodeFade, DelayMs, InactiveOpacity, MinimumContrast};
+use settings::{CenteredPaddingSettings, CodeFade, DelayMs, InactiveOpacity, MinimumContrast};
 use ui::prelude::*;
 
 #[derive(Debug, Default, Clone, Copy, PartialEq, Eq, Hash)]
@@ -71,6 +71,14 @@ impl_newtype_numeric_stepper!(CodeFade, 0.1, 0.2, 0.05, 0.0, 0.9);
 impl_newtype_numeric_stepper!(InactiveOpacity, 0.1, 0.2, 0.05, 0.0, 1.0);
 impl_newtype_numeric_stepper!(MinimumContrast, 1., 10., 0.5, 0.0, 106.0);
 impl_newtype_numeric_stepper!(DelayMs, 100, 500, 10, 0, 2000);
+impl_newtype_numeric_stepper!(
+    CenteredPaddingSettings,
+    0.05,
+    0.2,
+    0.1,
+    CenteredPaddingSettings::MIN_PADDING,
+    CenteredPaddingSettings::MAX_PADDING
+);
 
 macro_rules! impl_numeric_stepper_int {
     ($type:ident) => {