RFR: 8309751: Duplicate constant pool entries added during default method processing [v4]

[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.

Coleen Phillimore has updated the pull request incrementally with one additional commit since the last revision:

  Rename hash back and add a comment.

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Changes:
  - all: https://git.openjdk.org/jdk/pull/18548/files
  - new: https://git.openjdk.org/jdk/pull/18548/files/8e8059ab..d1b7d143

Webrevs:
 - full: https://webrevs.openjdk.org/?repo=jdk&pr=18548&range=03
 - incr: https://webrevs.openjdk.org/?repo=jdk&pr=18548&range=02-03

  Stats: 7 lines in 1 file changed: 2 ins; 0 del; 5 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