feat: migrate unit tests to Jest (#6353)

* config(jest): updated setup
* config(jest): update testMatch to include jsx files
* config(jest): add transformIgnorePatterns
* config(jest): update ignore files that do not work in jest yet
* config: add test:unit-jest to test script

* fix(jest): lint with eslint-plugin-jest

* refactor(jest): move unit test directory
* refactor(mocha): restore mocha tests that fail in jest

* docs(jest): update helpful scripts with test:unit-jest

test/unit/setup.js

@@ -0,0 +1,19 @@
+import win from "../../src/core/window"
+
+function copyProps(src, target) {
+  const props = Object.getOwnPropertyNames(src)
+    .filter(prop => typeof target[prop] === "undefined")
+    .reduce((result, prop) => ({
+      ...result,
+      [prop]: Object.getOwnPropertyDescriptor(src, prop),
+    }), {})
+  Object.defineProperties(target, props)
+}
+
+global.window = window
+global.document = window.document
+global.navigator = {
+  userAgent: "node.js",
+}
+copyProps(win, window) // use UI's built-in window wrapper
+copyProps(window, global)