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/documents/rich.rs

@@ -98,6 +98,7 @@ impl RenderOnce for RichTextEditor {
         };
         let (open_link, close_link) = (set_linking(true), set_linking(false));
         let float_id: ElementId = (self.id.clone(), "float").into();
+        let platform = cx.theme().platform;
         let floating = FloatingToolbar::new(float_id.clone(), &self.field).children(
             INLINE.iter().map(|tool_of| {
                 let on = pressed.contains(&tool_of.0);
@@ -107,6 +108,7 @@ impl RenderOnce for RichTextEditor {
                     *tool_of,
                     on,
                     Some(open_link.clone()),
+                    platform,
                 )
             }),
         );