Don't export platform::* from gpui

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

crates/gpui/src/elements/mouse_event_handler.rs

@@ -5,12 +5,13 @@ use crate::{
         vector::{vec2f, Vector2F},
     },
     platform::CursorStyle,
+    platform::MouseButton,
     scene::{
         CursorRegion, HandlerSet, MouseClick, MouseDown, MouseDownOut, MouseDrag, MouseHover,
         MouseMove, MouseMoveOut, MouseScrollWheel, MouseUp, MouseUpOut,
     },
     DebugContext, Element, ElementBox, EventContext, LayoutContext, MeasurementContext,
-    MouseButton, MouseRegion, MouseState, PaintContext, RenderContext, SizeConstraint, View,
+    MouseRegion, MouseState, PaintContext, RenderContext, SizeConstraint, View,
 };
 use serde_json::json;
 use std::{marker::PhantomData, ops::Range};

crates/gpui/src/elements/resizable.rs

@@ -4,8 +4,10 @@ use pathfinder_geometry::vector::{vec2f, Vector2F};
 use serde_json::json;
 
 use crate::{
-    geometry::rect::RectF, scene::MouseDrag, Axis, CursorStyle, Element, ElementBox,
-    ElementStateHandle, MouseButton, MouseRegion, RenderContext, View,
+    geometry::rect::RectF,
+    platform::{CursorStyle, MouseButton},
+    scene::MouseDrag,
+    Axis, Element, ElementBox, ElementStateHandle, MouseRegion, RenderContext, View,
 };
 
 use super::{ConstrainedBox, Hook};

crates/gpui/src/elements/uniform_list.rs

@@ -5,9 +5,10 @@ use crate::{
         vector::{vec2f, Vector2F},
     },
     json::{self, json},
+    platform::ScrollWheelEvent,
     presenter::MeasurementContext,
     scene::MouseScrollWheel,
-    ElementBox, MouseRegion, RenderContext, ScrollWheelEvent, View,
+    ElementBox, MouseRegion, RenderContext, View,
 };
 use json::ToJson;
 use std::{cell::RefCell, cmp, ops::Range, rc::Rc};