Undo/Redo buttons, refactor menu toggles (#793)

* Make Undo & Redo and the menu buttons into actions; add undo/redo buttons

* Create variables for the ToolIcon colors

* Darken the menu buttons when they’re active

* Put the more intensive test in `perform`

* Fix & restyle hint viewer

* Add pinch zoom for macOS Safari

* Chrome/Firefox trackpad pinch zoom

* openedMenu → openMenu

* needsShapeEditor.ts → showSelectedShapeActions.ts

* Call showSelectedShapeActions

src/types.ts

@@ -31,7 +31,7 @@ export type AppState = {
   selectedId?: string;
   isResizing: boolean;
   zoom: number;
-  openedMenu: "canvas" | "shape" | null;
+  openMenu: "canvas" | "shape" | null;
   lastPointerDownWith: PointerType;
 };
 
@@ -47,3 +47,8 @@ export type Gesture = {
   initialDistance: number | null;
   initialScale: number | null;
 };
+
+export declare class GestureEvent extends UIEvent {
+  readonly rotation: number;
+  readonly scale: number;
+}