RFR: 8248188: Add IntrinsicCandidate and API for Base64 decoding [v2]

[CoreyAshford]

On Mon, 5 Oct 2020 16:08:55 GMT, CoreyAshford <github.com+51754783+CoreyAshford at openjdk.org> wrote:

>> Nobody replied, so I suggest to leave aotCodeHeap.cpp as it was. AOT folks can add it when they need it.
>
>> Nobody replied, so I suggest to leave aotCodeHeap.cpp as it was. AOT folks can add it when they need it.
> 
> Ok, I will drop that change from that PR.  Thank you.

I have rebased this PR and made the requested changes.   The force push is only because of the rebase; I have preserved
the commit history.

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PR: https://git.openjdk.java.net/jdk/pull/293