add theme titlebar height and app-owned strip dragging

crates/theme/src/source/windows.rs

@@ -16,6 +16,8 @@ use crate::system::{AccessibilityPreferences, PartialPalette, SourceKind, System
 const CONTROL_RADIUS_PX: f32 = 4.0;
 /// WinUI 11's default text-box height, in pixels at 100% scaling.
 const INPUT_HEIGHT_PX: f32 = 32.0;
+/// The window caption's height, in pixels at 100% scaling, as Win32 reports it.
+const TITLEBAR_HEIGHT_PX: f32 = 32.0;
 /// WinUI 11's default body text size, in pixels at 100% scaling.
 const ROOT_FONT_SIZE_PX: f32 = 14.0;
 
@@ -158,6 +160,7 @@ impl ThemeSource for WindowsSource {
             },
             control_radius: Some(gpui::px(CONTROL_RADIUS_PX)),
             input_height: Some(gpui::px(INPUT_HEIGHT_PX)),
+            titlebar_height: Some(gpui::px(TITLEBAR_HEIGHT_PX)),
             root_font_size: Some(gpui::px(ROOT_FONT_SIZE_PX * text_scale as f32)),
             accessibility: self.accessibility(),
             source: SourceKind::Windows,