Add findlast shim for outdated browsers (#1463)

* Add findlast shim for crappy browsers

* Fix types

src/platform/polyfills.web.ts

@@ -1,5 +1,9 @@
+// @ts-ignore no decl -prf
+import * as findLast from 'array.prototype.findlast'
 /// <reference lib="dom" />
 
+findLast.shim()
+
 // @ts-ignore whatever typescript wants to complain about here, I dont care about -prf
 window.setImmediate = (cb: () => void) => setTimeout(cb, 0)