RFR: 8372258: Improve TypeVariable support [v3]

[Per Minborg]

> The `TypeVariableImpl::getGenericDeclaration` method should return copies of generic declarations where appropriate.

Per Minborg has updated the pull request incrementally with one additional commit since the last revision:

  Update copyright year

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Changes:
  - all: https://git.openjdk.org/jdk/pull/28429/files
  - new: https://git.openjdk.org/jdk/pull/28429/files/ba7f093f..7d3fee14

Webrevs:
 - full: https://webrevs.openjdk.org/?repo=jdk&pr=28429&range=02
 - incr: https://webrevs.openjdk.org/?repo=jdk&pr=28429&range=01-02

  Stats: 1 line in 1 file changed: 0 ins; 0 del; 1 mod
  Patch: https://git.openjdk.org/jdk/pull/28429.diff
  Fetch: git fetch https://git.openjdk.org/jdk.git pull/28429/head:pull/28429

PR: https://git.openjdk.org/jdk/pull/28429