Theme · Platform: one platform for buttons and caps, icon themes, frosted panes

theme::Platform moves out of typography and shell's ControlsStyle folds
into it; the theme's platform starts as the system's. Window buttons Ely
draws, the title bar's layout and every key cap follow it, secondary
included, through typography::keys::keystroke; a title bar whose buttons
the OS draws follows the OS. primitives::IconTheme lays an owner's rules
by file name and extension over Ely's map, for every file icon.
shell::Vibrancy fills a pane with the palette's new glass, translucent
so a window opened Blurred shows its backdrop, solid under high contrast.
gpui 0.2.2 has no Mica; that line stays blocked.

src/shell/mod.rs

@@ -11,11 +11,12 @@ mod tabs;
 #[cfg(all(test, feature = "test-support"))]
 mod tests;
 mod update;
+mod vibrancy;
 mod windows;
 
 pub use activity::{ActivityBar, ActivityItem};
 pub use bars::{StatusBar, StatusBarItem, Toolbar, ToolbarGroup, ToolbarSeparator};
-pub use chrome::{ControlsStyle, TitleBar, WindowControls, drag_region};
+pub use chrome::{TitleBar, WindowControls, drag_region};
 pub use crash::CrashReporter;
 pub use dialogs::{AboutDialog, SplashScreen};
 pub use frame::ResizeBorder;
@@ -25,4 +26,5 @@ pub use status::{Connectivity, OfflineIndicator, ZoomControl};
 pub use switcher::WindowSwitcher;
 pub use tabs::{TabBar, WindowTab};
 pub use update::{UpdateBanner, UpdateDialog, UpdateState};
+pub use vibrancy::Vibrancy;
 pub use windows::{Corner, Hosted, MiniWindow, WindowManager, open_hosted};