RFR: 8297777: jdk.jlink StringSharingPlugin uses com.sun.tools.classfile library

[Qing Xiao]

Migrate jdk.jlink StringSharingPlugin to use new classfile library

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Commit messages:
 - Migrate jdk.jlink StringSharingPlugin to use new classfile library

Changes: https://git.openjdk.org/jdk/pull/15408/files
 Webrev: https://webrevs.openjdk.org/?repo=jdk&pr=15408&range=00
  Issue: https://bugs.openjdk.org/browse/JDK-8297777
  Stats: 126 lines in 1 file changed: 12 ins; 54 del; 60 mod
  Patch: https://git.openjdk.org/jdk/pull/15408.diff
  Fetch: git fetch https://git.openjdk.org/jdk.git pull/15408/head:pull/15408

PR: https://git.openjdk.org/jdk/pull/15408