RFR: 8339635: StringConcatFactory optimization for CompactStrings off

[Shaojin Wen]

A small optimization, when CompactStrings is turned off, the coder method is not generated, which improves the startup performance

-------------

Commit messages:
 - Update src/java.base/share/classes/java/lang/invoke/StringConcatFactory.java
 - Update src/java.base/share/classes/java/lang/invoke/StringConcatFactory.java
 - optimize for CompactStrings is off

Changes: https://git.openjdk.org/jdk/pull/20722/files
  Webrev: https://webrevs.openjdk.org/?repo=jdk&pr=20722&range=00
  Issue: https://bugs.openjdk.org/browse/JDK-8339635
  Stats: 12 lines in 3 files changed: 11 ins; 0 del; 1 mod
  Patch: https://git.openjdk.org/jdk/pull/20722.diff
  Fetch: git fetch https://git.openjdk.org/jdk.git pull/20722/head:pull/20722

PR: https://git.openjdk.org/jdk/pull/20722