Convert tests that parse an Extensions sequence to instead

net/data/parse_certificate_unittest/v3_certificate_template.txt

 # This is cert.pem from BoringSSL's tests.
 # https://boringssl.googlesource.com/boringssl/+/5acc423517ec9d53e6cf2cd1b968405e0972c745/ssl/test/runner/cert.pem
 
 # This file is itself valid ascii-der, however uses comments to name various
 # sections (using BEGIN and END). These named sections can be overlapping, and
 # are replaced for generating various test data.
 
 SEQUENCE {
   SEQUENCE {
     [0] {
@@ skipping 63 matching lines @@
       }
       BIT_STRING {
         `00`
         SEQUENCE {
           INTEGER { `00d82bc8a632e462ff4df3d0ad598b45a7bdf147bf09587b22bd35ae97258694a080c0b41f7691674631d01084b7221e70239172c8e96d793a8577800fc4951675c54a714cc8633fa3f2639c2a4f9afacbc1716e288528a0271e651cae07d55b6f2d43ed2b90b18caf246daee9173a05c1bfb81cae653b1b58c2d9aed6aa6788f1` }
           INTEGER { 65537 }
         }
       }
     }
     [3] {
+#-----BEGIN EXTENSIONS-----
       SEQUENCE {
         SEQUENCE {
           # subjectKeyIdentifier
           OBJECT_IDENTIFIER { 2.5.29.14 }
           OCTET_STRING {
             OCTET_STRING { `8b75d5accb08be0e1f65b7fa56be6ca775da85af` }
           }
         }
         SEQUENCE {
           # authorityKeyIdentifier
@@ skipping 13 matching lines @@
             SEQUENCE {
               BOOLEAN { `ff` }
             }
 #-----END BASIC_CONSTRAINTS-----
           }
         }
 #-----BEGIN EXTENSION-----
 # (For adding in another extension at the end of the list)
 #-----END EXTENSION-----
       }
+#-----END EXTENSIONS-----
     }
   }
   SEQUENCE {
     # sha1WithRSAEncryption
     OBJECT_IDENTIFIER { 1.2.840.113549.1.1.5 }
     NULL {}
   }
   BIT_STRING { `003be8786d95d63d6af713192c1bc288ae22abf48d32f57c7167cf2dd11cc2c387e2e9be895ce434ab4891c23f95ae2b479e25786b4f9a10a472fdcff7020cb00a08a45ae2e5747e111d39606ac91f69f32e6326dc9eef6b7a0ae1545798aa729178047e1f8f654d1f0b12ac9c240f84141a552d1fbbf09d09b2085c5932658026` }
 }