RFR: 8263776: [JVMCI] add helper to perform Java upcalls

[Tom Rodriguez]

On Thu, 18 Mar 2021 06:30:49 GMT, Tom Rodriguez <never at openjdk.org> wrote:

> 8263776: [JVMCI] add helper to perform Java upcalls

I had pushed the wrong version of this in the initial commit but it's now the correct one.  There were changes to SignatureIterator that needs accommodation and I'd pushed an older version of this fix.

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PR: https://git.openjdk.java.net/jdk/pull/3067