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/collab_ui/src/collab_titlebar_item.rs

@@ -14,7 +14,7 @@ use std::sync::Arc;
 use theme::ActiveTheme;
 use ui::{
     h_flex, popover_menu, prelude::*, Avatar, AvatarAudioStatusIndicator, Button, ButtonLike,
-    ButtonStyle, ContextMenu, Icon, IconButton, IconName, PlatformTitlebar, TintColor, Tooltip,
+    ButtonStyle, ContextMenu, Icon, IconButton, IconName, TintColor, TitleBar, Tooltip,
 };
 use util::ResultExt;
 use vcs_menu::{build_branch_list, BranchList, OpenRecent as ToggleVcsMenu};
@@ -58,8 +58,7 @@ impl Render for CollabTitlebarItem {
         let project_id = self.project.read(cx).remote_id();
         let workspace = self.workspace.upgrade();
 
-        PlatformTitlebar::new("collab-titlebar")
-            .background(cx.theme().colors().title_bar_background)
+        TitleBar::new("collab-titlebar")
             // note: on windows titlebar behaviour is handled by the platform implementation
             .when(cfg!(not(windows)), |this| {
                 this.on_click(|event, cx| {