ui: Refine TitleBar component (#9415)

This PR continues the refinements to the `TitleBar` component.

Here are the notable changes:

- `KeyBindingDisplay` and `PlatformStyle` have been unified into a
single `PlatformStyle`.
- This provides us a consistent way for adapting UI to different
platform styles.
- `PlatformTitlebar` has been renamed to `TitleBar`.
  - The `Platform` prefix was irrelevant.
- The Windows window controls have been factored out into a separate
module and have been componentized.

<img width="1283" alt="Screenshot 2024-03-15 at 3 34 38 PM"
src="https://github.com/zed-industries/zed/assets/1486634/07da391f-828b-48bf-8849-58863f4ccce7">

> I'm missing the Segoe Fluent Icons font, so that's why the aren't
rendering properly.

Release Notes:

- N/A

crates/ui/src/components/stories.rs

@@ -10,9 +10,9 @@ mod label;
 mod list;
 mod list_header;
 mod list_item;
-mod platform_titlebar;
 mod tab;
 mod tab_bar;
+mod title_bar;
 mod toggle_button;
 
 pub use avatar::*;
@@ -27,7 +27,7 @@ pub use label::*;
 pub use list::*;
 pub use list_header::*;
 pub use list_item::*;
-pub use platform_titlebar::*;
 pub use tab::*;
 pub use tab_bar::*;
+pub use title_bar::*;
 pub use toggle_button::*;