RFR: 8309751: Duplicate constant pool entries added during default method processing

[Coleen Phillimore]

This uses Ashutosh's patch to avoid adding duplicate constant pool entries during default method processing, with one change to make it conditional if not needed. I tested this locally and started writing a test, but writing a test is more difficult because duplicate constant pool entries don't actually violate the spec.

Tested with tier1-4 and ran some startup performance benchmarks on the patch.

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Commit messages:
 - 8309751: Duplicate constant pool entries added during default method processing

Changes: https://git.openjdk.org/jdk/pull/18548/files
  Webrev: https://webrevs.openjdk.org/?repo=jdk&pr=18548&range=00
  Issue: https://bugs.openjdk.org/browse/JDK-8309751
  Stats: 63 lines in 3 files changed: 44 ins; 1 del; 18 mod
  Patch: https://git.openjdk.org/jdk/pull/18548.diff
  Fetch: git fetch https://git.openjdk.org/jdk.git pull/18548/head:pull/18548

PR: https://git.openjdk.org/jdk/pull/18548