[code-reflection] Integrated: Add BlockGroup experiment

[Gary Frost]

Added experimental  code for creating arbitrarty blocks of code 


java @.bld 
jjava @.exp ffi-opencl BlockGroup

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Commit messages:
 - Add BlockGroup experiment

Changes: https://git.openjdk.org/babylon/pull/826/files
  Webrev: https://webrevs.openjdk.org/?repo=babylon&pr=826&range=00
  Stats: 132 lines in 4 files changed: 132 ins; 0 del; 0 mod
  Patch: https://git.openjdk.org/babylon/pull/826.diff
  Fetch: git fetch https://git.openjdk.org/babylon.git pull/826/head:pull/826

PR: https://git.openjdk.org/babylon/pull/826