Don't export platform::* from gpui

I'd like to avoid cluttering the top-level namespace with all the platform-
specific types.

crates/picker/src/picker.rs

@@ -3,9 +3,9 @@ use gpui::{
     elements::*,
     geometry::vector::{vec2f, Vector2F},
     keymap_matcher::KeymapContext,
-    platform::CursorStyle,
-    AnyViewHandle, AppContext, Axis, Entity, MouseButton, MouseState, RenderContext, Task, View,
-    ViewContext, ViewHandle, WeakViewHandle,
+    platform::{CursorStyle, MouseButton},
+    AnyViewHandle, AppContext, Axis, Entity, MouseState, RenderContext, Task, View, ViewContext,
+    ViewHandle, WeakViewHandle,
 };
 use menu::{Cancel, Confirm, SelectFirst, SelectIndex, SelectLast, SelectNext, SelectPrev};
 use parking_lot::Mutex;