Set displayName for Fantom configuration (#52778)

Summary:
Pull Request resolved: #52778

Changelog: [internal]

Jest has an option to select a specific project when running tests:

```
jest --selectProjects fantom
```

But for this to work, a `displayName` option needs to be set in the project configuration. This adds that for Fantom tests (using `fantom`).

Reviewed By: rshest

Differential Revision: D78802516

fbshipit-source-id: 483e7c1450b1f97961e4e43c963fac3ce82cee58

Author: rubennorte

private/react-native-fantom/config/jest.config.js

@@ -23,6 +23,7 @@ const globalSetup /*: ?string */ = isCI
   : null;
 
 module.exports = {
+  displayName: 'fantom',
   rootDir: path.resolve(__dirname, '../../..') /*:: as string */,
   roots: [
     '<rootDir>/packages/react-native',