[code-reflection] RFR: Concat Transform Optimizations

[Ian Graves]

Updates to the transformation on Concats to StringBuilder that reduce redundant "new" StringBuilders while respecting correctness.

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Commit messages:
 - Cleanup
 - Updates reducing redundant StringBuilders

Changes: https://git.openjdk.org/babylon/pull/149/files
  Webrev: https://webrevs.openjdk.org/?repo=babylon&pr=149&range=00
  Stats: 39 lines in 1 file changed: 21 ins; 4 del; 14 mod
  Patch: https://git.openjdk.org/babylon/pull/149.diff
  Fetch: git fetch https://git.openjdk.org/babylon.git pull/149/head:pull/149

PR: https://git.openjdk.org/babylon/pull/149