In getFlutterRoot(), scripts loaded via data: URIs are URI encoded.
getFlutterRoot() scans the contents of the data for the file:// URI path
of the Flutter SDK, which itself is URI-encoded. The end result is that
if the SDK path contains a space, the embedded file:// URI will contain
a %20. When this is encoded in a data: URI, the contents are
URI-encoded, resulting in %2520, since the % is encoded to %25.

This patch decodes the data: URI before extracting the SDK file:// URI.