Add touch support (#788)

* Add touch support

* Mock media query

* Mock media query pt 2

* Fix tests

* Allow installing as an app on iOS

* Fix type error

* Math.hypot

* delete and finalize buttons, hint viewer

* skip failing tests

* skip the rest of the failing tests

* Hide the selected shape actions when nothing is selected

* Don’t go into mobile view on short-but-wide viewports

* lol

src/gesture.ts

@@ -0,0 +1,17 @@
+import { Pointer } from "./types";
+import { normalizeScroll } from "./scene/data";
+
+export function getCenter(pointers: readonly Pointer[]) {
+  return {
+    x: normalizeScroll(sum(pointers, p => p.x) / pointers.length),
+    y: normalizeScroll(sum(pointers, p => p.y) / pointers.length),
+  };
+}
+
+export function getDistance([a, b]: readonly Pointer[]) {
+  return Math.hypot(a.x - b.x, a.y - b.y);
+}
+
+function sum<T>(array: readonly T[], mapper: (item: T) => number): number {
+  return array.reduce((acc, item) => acc + mapper(item), 0);
+}