Add script that generates X509 certificates for testing dart:io SecureSocket

tests/standalone/io/intermediate_authority_v3_extensions

Index: tests/standalone/io/intermediate_authority_v3_extensions
diff --git a/runtime/lib/developer_sources.gypi b/tests/standalone/io/intermediate_authority_v3_extensions
similarity index 52%
copy from runtime/lib/developer_sources.gypi
copy to tests/standalone/io/intermediate_authority_v3_extensions
index e3f1ea658789977f908c65204ae033f2701a5032..8d0f70c03a8581f479a2cae12641dc1b19471d55 100644
--- a/runtime/lib/developer_sources.gypi
+++ b/tests/standalone/io/intermediate_authority_v3_extensions
@@ -2,16 +2,10 @@
 # for details. All rights reserved. Use of this source code is governed by a
 # BSD-style license that can be found in the LICENSE file.
 
-# Sources visible via dart:developer library.
+# OpenSSL configuration file giving the v3 extensions for an intermediate
+# certificate authority.
 
-{
-  'sources': [
-    'developer.cc',
-    'developer.dart',
-    'profiler.cc',
-    'profiler.dart',
-    'timeline.cc',
-    'timeline.dart',
-  ],
-}
+basicConstraints = CA:true
+subjectKeyIdentifier=hash
+authorityKeyIdentifier=keyid:always,issuer