RFR: 8339683: Simplify class data generation in InvokerBytecodeGenerator

[Chen Liang]

Elide duplicate field CP entry creation, and reuse elements in the field CP entry for field generation.

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Commit messages:
 - 8339683: Simplify class data generation in InvokerBytecodeGenerator

Changes: https://git.openjdk.org/jdk/pull/20896/files
  Webrev: https://webrevs.openjdk.org/?repo=jdk&pr=20896&range=00
  Issue: https://bugs.openjdk.org/browse/JDK-8339683
  Stats: 65 lines in 1 file changed: 7 ins; 32 del; 26 mod
  Patch: https://git.openjdk.org/jdk/pull/20896.diff
  Fetch: git fetch https://git.openjdk.org/jdk.git pull/20896/head:pull/20896

PR: https://git.openjdk.org/jdk/pull/20896