refactor!: Switch default bundle type to endoZipBase64

*BREAKING CHANGE*: This change switches the default bundle format from
`nestedEvaluate` to `endoZipBase64`.
The new bundle format has a fundamentally different shape and content,
so any existing code that depends on being able to inspect the `source`
string of the bundle will break.
This functionality will be replaced with a new feature for
consistent-hash integrity checking. #3859

packages/bundle-source/src/index.js

@@ -15,7 +15,7 @@ import { SourceMapConsumer } from 'source-map';
 
 import './types.js';
 
-const DEFAULT_MODULE_FORMAT = 'nestedEvaluate';
+const DEFAULT_MODULE_FORMAT = 'endoZipBase64';
 const DEFAULT_FILE_PREFIX = '/bundled-source/...';
 const SUPPORTED_FORMATS = ['getExport', 'nestedEvaluate', 'endoZipBase64'];