RFR: 8359707: Add classfile modification code to RedefineClassHelper [v7]

[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.

Coleen Phillimore has updated the pull request incrementally with two additional commits since the last revision:

 - Update test/lib/RedefineClassHelper.java
   
   Co-authored-by: David Holmes <62092539+dholmes-ora at users.noreply.github.com>
 - Fix imports

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Changes:
  - all: https://git.openjdk.org/jdk/pull/25857/files
  - new: https://git.openjdk.org/jdk/pull/25857/files/3285f4d5..21223e37

Webrevs:
 - full: https://webrevs.openjdk.org/?repo=jdk&pr=25857&range=06
 - incr: https://webrevs.openjdk.org/?repo=jdk&pr=25857&range=05-06

  Stats: 7 lines in 1 file changed: 1 ins; 3 del; 3 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