Use custom ClientRect interface

Closes #251

shared/src/dom/client-rect.d.ts

@@ -0,0 +1,8 @@
+export declare interface ClientRect {
+    bottom: number;
+    readonly height: number;
+    left: number;
+    right: number;
+    top: number;
+    readonly width: number;
+}

shared/src/dom/index.ts

@@ -0,0 +1 @@
+export { ClientRect } from './client-rect';