RFR: 8249783: Simplify DerValue and DerInputStream [v2]

[Weijun Wang]

On Sat, 26 Sep 2020 00:57:23 GMT, Weijun Wang <weijun at openjdk.org> wrote:

>> Weijun Wang has updated the pull request incrementally with one additional commit since the last revision:
>> 
>>   Enhance DerValue::getOctetString to be able to read multi-level constructed value.
>
> Thanks a lot for your detailed code review. I'll push a new commit early next week.

New change pushed. I haven't really moved the "deprecated" codes together in DerValue. I just put the data-related and
tag-related methods together and add more comments.

Besides following your suggestions in the comment, this time I made some fine tuned changes for indefinite length
parsing, esp, for the uncertainty about remaining data after conversion. in the future, we can enhance
DerIndefLenConverter to be more precise and efficient.

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PR: https://git.openjdk.java.net/jdk/pull/232