[code-reflection] Integrated: More OpHelper maintenance

[Gary Frost]

Added instanceOp to field and invoke helpers.  This simplifies finding invokes throw VarOps.

Also adde VarOp helper and rationalized names

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Commit messages:
 - More OpHelper maintenance

Changes: https://git.openjdk.org/babylon/pull/821/files
  Webrev: https://webrevs.openjdk.org/?repo=babylon&pr=821&range=00
  Stats: 506 lines in 24 files changed: 148 ins; 147 del; 211 mod
  Patch: https://git.openjdk.org/babylon/pull/821.diff
  Fetch: git fetch https://git.openjdk.org/babylon.git pull/821/head:pull/821

PR: https://git.openjdk.org/babylon/pull/821