RFR: 8359707: Add classfile modification code to RedefineClassHelper [v6]

[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 one additional commit since the last revision:

  Made it even shorter.

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Changes:
  - all: https://git.openjdk.org/jdk/pull/25857/files
  - new: https://git.openjdk.org/jdk/pull/25857/files/a8ed67c0..3285f4d5

Webrevs:
 - full: https://webrevs.openjdk.org/?repo=jdk&pr=25857&range=05
 - incr: https://webrevs.openjdk.org/?repo=jdk&pr=25857&range=04-05

  Stats: 4 lines in 1 file changed: 0 ins; 3 del; 1 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