polyfill structuredclone on legacy browsers

Fixes APP-T4SK

src/platform/polyfills.web.test.ts

@@ -0,0 +1,29 @@
+import {RichText} from '@bsky/sdk/richtext'
+
+describe('web polyfills', () => {
+  const nativeStructuredClone = globalThis.structuredClone
+
+  afterEach(() => {
+    globalThis.structuredClone = nativeStructuredClone
+  })
+
+  it('supports rich text when structuredClone is unavailable', async () => {
+    Reflect.deleteProperty(globalThis, 'structuredClone')
+
+    let structuredCloneReady: Promise<void> | undefined
+    jest.isolateModules(() => {
+      const polyfills =
+        require('./polyfills.web') as typeof import('./polyfills.web')
+      structuredCloneReady = polyfills.structuredCloneReady
+    })
+    await structuredCloneReady
+
+    const richText = new RichText(
+      {text: 'hello\n\n\nworld'},
+      {cleanNewlines: true},
+    )
+
+    expect(richText.text).toBe('hello\n\nworld')
+    expect(richText.clone()).toEqual(richText)
+  })
+})

src/platform/polyfills.web.ts

@@ -1,6 +1,16 @@
 import 'array.prototype.findlast/auto'
 import 'setimmediate'
 
+export const structuredCloneReady: Promise<void> =
+  typeof globalThis.structuredClone === 'function'
+    ? Promise.resolve()
+    : import('@ungap/structured-clone').then(({default: structuredClone}) => {
+        if (typeof globalThis.structuredClone !== 'function') {
+          globalThis.structuredClone =
+            structuredClone as typeof globalThis.structuredClone
+        }
+      })
+
 if (process.env.NODE_ENV !== 'production') {
   // In development, react-native-web's <View> tries to validate that
   // text is wrapped into <Text>. It doesn't catch all cases but is useful.
@@ -30,5 +40,3 @@ if (process.env.NODE_ENV !== 'production') {
     }
   }
 }
-
-export {}