[code-reflection] Integrated: Added a pair of jsplitpanes to FuncOpViewer

[Gary Frost]

This allows the left and right textpanes in FuncOpViewer  to be resized.

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Commit messages:
 - Added a pair of jsplitpanes to FuncOpViewer

Changes: https://git.openjdk.org/babylon/pull/502/files
  Webrev: https://webrevs.openjdk.org/?repo=babylon&pr=502&range=00
  Stats: 12 lines in 1 file changed: 8 ins; 0 del; 4 mod
  Patch: https://git.openjdk.org/babylon/pull/502.diff
  Fetch: git fetch https://git.openjdk.org/babylon.git pull/502/head:pull/502

PR: https://git.openjdk.org/babylon/pull/502