[code-reflection] Integrated: Added hatless nbody example

[Gary Frost]

Mainly this allows us to test jextract and to compare numbers against an eventual hat implementation
 
 We are also setting the stage forn opencl backend implementation leaning on the extracted opencl.
 
 You will need to modify bld to jextract opencl and opengl  
 
 ```
 java @bldr/hatlessrun nbody
 ```

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Commit messages:
 - Added hatless nbody example to test jextract and to compare numbers against hat implementation

Changes: https://git.openjdk.org/babylon/pull/288/files
  Webrev: https://webrevs.openjdk.org/?repo=babylon&pr=288&range=00
  Stats: 1236 lines in 10 files changed: 1233 ins; 0 del; 3 mod
  Patch: https://git.openjdk.org/babylon/pull/288.diff
  Fetch: git fetch https://git.openjdk.org/babylon.git pull/288/head:pull/288

PR: https://git.openjdk.org/babylon/pull/288