RFR: 8338937: Optimize the string concatenation of ClassDesc

[Shaojin Wen]

Optimize ClassDesc related string concatenation, which will reduce object allocation during startup.

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Commit messages:
 - Optimize the string concatenation related to ClassDesc during startup

Changes: https://git.openjdk.org/jdk/pull/20705/files
  Webrev: https://webrevs.openjdk.org/?repo=jdk&pr=20705&range=00
  Issue: https://bugs.openjdk.org/browse/JDK-8338937
  Stats: 46 lines in 6 files changed: 35 ins; 0 del; 11 mod
  Patch: https://git.openjdk.org/jdk/pull/20705.diff
  Fetch: git fetch https://git.openjdk.org/jdk.git pull/20705/head:pull/20705

PR: https://git.openjdk.org/jdk/pull/20705