RFR: 8246797: A convenient method to read OPTIONAL element [v3]

[Weijun Wang]

On Tue, 24 Aug 2021 22:15:52 GMT, Weijun Wang <weijun at openjdk.org> wrote:

>> This code change adds new methods to `DerInputStream` to easily and safely read optional fields in a ASN.1 DER-encoded value. It also adds several wrapping methods to `DerValue` to avoid unnecessary memory copying when calling by an internal method.
>> 
>> The new methods are applied to `OAEPParameters` to show out how they work. A new regression test is added to show that not only the new methods are simper but they are safer and more correct.
>
> Weijun Wang has updated the pull request incrementally with one additional commit since the last revision:
> 
>   new APIs and new examples

New commit pushed. New APIs for reading non-context specific OPTIONAL field and sub-values of a DerValue. Also updated 2 classes to showcase the new methods.

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PR: https://git.openjdk.java.net/jdk/pull/5221