settings ui: Use font picker element from onboarding instead of editor for font components (#39593)

The font picker from onboarding is a lot friendlier to interact with and
makes it impossible for a user to select an invalid font from the
settings ui.

I also moved the font picker from the onboarding crate to the ui_input
crate

## New Look
<img width="1136" height="812" alt="image"
src="https://github.com/user-attachments/assets/7436682c-6a41-4860-a18b-13e15b8f3f31"
/>

Release Notes:

- N/A

crates/ui_input/src/ui_input.rs

@@ -4,10 +4,12 @@
 //!
 //! It can't be located in the `ui` crate because it depends on `editor`.
 //!
+mod font_picker;
 mod numeric_stepper;
 
 use component::{example_group, single_example};
 use editor::{Editor, EditorElement, EditorStyle};
+pub use font_picker::*;
 use gpui::{App, Entity, FocusHandle, Focusable, FontStyle, Hsla, Length, TextStyle};
 pub use numeric_stepper::*;
 use settings::Settings;