RFR: 8341900: Optimize DirectCodeBuilder writeBody

[Shaojin Wen]

A simple optimization to reduce duplicate code. Reduce the codeSize of writeBody from 268 to 240

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Commit messages:
 - optimize writeBody

Changes: https://git.openjdk.org/jdk/pull/21440/files
  Webrev: https://webrevs.openjdk.org/?repo=jdk&pr=21440&range=00
  Issue: https://bugs.openjdk.org/browse/JDK-8341900
  Stats: 18 lines in 1 file changed: 5 ins; 10 del; 3 mod
  Patch: https://git.openjdk.org/jdk/pull/21440.diff
  Fetch: git fetch https://git.openjdk.org/jdk.git pull/21440/head:pull/21440

PR: https://git.openjdk.org/jdk/pull/21440