RFR: 8336267: Method and Constructor signature parsing can be shared on the root object

[Chen Liang]

A straightforward optimization, to share the signature parsing of method, constructor, and field between the root and the copied objects, like how method handle accessors are shared.

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Commit messages:
 - 8336267: Method and Constructor signature parsing can be shared on the root object

Changes: https://git.openjdk.org/jdk/pull/20179/files
  Webrev: https://webrevs.openjdk.org/?repo=jdk&pr=20179&range=00
  Issue: https://bugs.openjdk.org/browse/JDK-8336267
  Stats: 31 lines in 3 files changed: 20 ins; 0 del; 11 mod
  Patch: https://git.openjdk.org/jdk/pull/20179.diff
  Fetch: git fetch https://git.openjdk.org/jdk.git pull/20179/head:pull/20179

PR: https://git.openjdk.org/jdk/pull/20179