RFR: 8296736: Some PKCS9Attribute can be created but cannot be encoded

[Weijun Wang]

One `PKCS9Attribute` can be created but cannot be encoded. Since the `SigningCertificateInfo::parse` method has not fully parsed the data (`PolicyInformation` is left out), this code change add the encoding itself as a field to the `SigningCertificateInfo` class so we can encode it.

After this change, unsupported `PKCSAttribute` object simply cannot be created. The `new(DerValue)` constructor rejects them (type 9-13, 15) in a `switch` block, and the `new(ObjectIdentifier, Object)` constructor rejects them because `VALUE_CLASSES` for them are null.

In the `encode()` method, we now throw `IllegalArgumentException` for these types and they will not happen.

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Commit messages:
 - avoid NPE
 - the fix

Changes: https://git.openjdk.org/jdk/pull/11070/files
 Webrev: https://webrevs.openjdk.org/?repo=jdk&pr=11070&range=00
  Issue: https://bugs.openjdk.org/browse/JDK-8296736
  Stats: 31 lines in 3 files changed: 18 ins; 0 del; 13 mod
  Patch: https://git.openjdk.org/jdk/pull/11070.diff
  Fetch: git fetch https://git.openjdk.org/jdk pull/11070/head:pull/11070

PR: https://git.openjdk.org/jdk/pull/11070