[change] Add usePlatformMethods to implement instance methods

A hook equivalent for implementing "native methods" on refs to elements backed
by function components.

scripts/jest/config.js

@@ -10,7 +10,7 @@ module.exports = {
   // resetMocks: true,
   rootDir: process.cwd(),
   roots: ['<rootDir>/packages'],
-  setupFiles: ['jest-canvas-mock'],
+  setupFiles: ['jest-canvas-mock', require.resolve('./setupFiles.js')],
   setupFilesAfterEnv: [require.resolve('./setupFramework.js')],
   snapshotSerializers: ['enzyme-to-json/serializer'],
   testEnvironment: 'jsdom',

scripts/jest/setupFiles.js

@@ -0,0 +1,10 @@
+/* eslint-env jasmine, jest */
+
+// JSDOM doesn't implement ResizeObserver
+class ResizeObserver {
+  disconnect() {}
+  observe() {}
+  unobserve() {}
+}
+
+window.ResizeObserver = ResizeObserver;