[code-reflection] Integrated: Added some more common OpHelpers

[Gary Frost]

Added a few more OpHelpers for Lambda, Statement, VarAccess and nested/sealed  them inside OpHelper.

-------------

Commit messages:
 - Added some more common OpHelpers

Changes: https://git.openjdk.org/babylon/pull/812/files
  Webrev: https://webrevs.openjdk.org/?repo=babylon&pr=812&range=00
  Stats: 1275 lines in 32 files changed: 435 ins; 689 del; 151 mod
  Patch: https://git.openjdk.org/babylon/pull/812.diff
  Fetch: git fetch https://git.openjdk.org/babylon.git pull/812/head:pull/812

PR: https://git.openjdk.org/babylon/pull/812