RFR: 8263776: [JVMCI] add helper to perform Java upcalls [v2]

[Tom Rodriguez]

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

Tom Rodriguez has refreshed the contents of this pull request, and previous commits have been removed. The incremental views will show differences compared to the previous content of the PR. The pull request contains two new commits since the last revision:

 - Review comments
 - 8263776: [JVMCI] add helper to perform Java upcalls

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Changes:
  - all: https://git.openjdk.java.net/jdk/pull/3067/files
  - new: https://git.openjdk.java.net/jdk/pull/3067/files/d24bd0d8..0a3b1bfa

Webrevs:
 - full: https://webrevs.openjdk.java.net/?repo=jdk&pr=3067&range=01
 - incr: https://webrevs.openjdk.java.net/?repo=jdk&pr=3067&range=00-01

  Stats: 33 lines in 1 file changed: 7 ins; 1 del; 25 mod
  Patch: https://git.openjdk.java.net/jdk/pull/3067.diff
  Fetch: git fetch https://git.openjdk.java.net/jdk pull/3067/head:pull/3067

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