RFR: 8334437: De-duplicate ProxyMethod list creation

[Claes Redestad]

Simple refactoring to extract identical, simple lambda expressions. Improve code clarity and reduce classes generated.

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Commit messages:
 - Simplify
 - Refactor ProxyMethod list creation

Changes: https://git.openjdk.org/jdk/pull/19760/files
  Webrev: https://webrevs.openjdk.org/?repo=jdk&pr=19760&range=00
  Issue: https://bugs.openjdk.org/browse/JDK-8334437
  Stats: 10 lines in 1 file changed: 4 ins; 4 del; 2 mod
  Patch: https://git.openjdk.org/jdk/pull/19760.diff
  Fetch: git fetch https://git.openjdk.org/jdk.git pull/19760/head:pull/19760

PR: https://git.openjdk.org/jdk/pull/19760