RFR: 8359707: Add classfile modification code to RedefineClassHelper

[Coleen Phillimore]

I copied this code for another test in the Valhalla repo and thought it would be a good utility function.  It might be better written using the Classfile API.
Tested with test.

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Commit messages:
 - 8359707: Add classfile modification code to RedefineClassHelper

Changes: https://git.openjdk.org/jdk/pull/25857/files
  Webrev: https://webrevs.openjdk.org/?repo=jdk&pr=25857&range=00
  Issue: https://bugs.openjdk.org/browse/JDK-8359707
  Stats: 98 lines in 2 files changed: 53 ins; 43 del; 2 mod
  Patch: https://git.openjdk.org/jdk/pull/25857.diff
  Fetch: git fetch https://git.openjdk.org/jdk.git pull/25857/head:pull/25857

PR: https://git.openjdk.org/jdk/pull/25857