Update composer to preview external link cards (#52)

* Fetch external link metadata during compose so the user can preview and remove the embed

* Add missing mocks

* Update tests to match recent changes

__tests__/lib/images.test.ts

@@ -54,7 +54,7 @@ describe('downloadAndResize', () => {
       100,
       100,
       'JPEG',
-      1,
+      100,
       undefined,
       undefined,
       undefined,

__tests__/view/com/composer/ComposePost.test.tsx

@@ -63,6 +63,7 @@ describe('ComposePost', () => {
       mockedRootStore,
       'testing publish',
       'testUri',
+      undefined,
       [],
       new Set<string>(),
       expect.anything(),