RFR: 8332100: Add missing `@since` to KeyValue::EC_TYPE in `java.xml.crypto`

[Nizar Benalla]

Simple code cleanup.
This was added back in [JDK 13](https://github.com/openjdk/jdk/commit/71825293eb83d7c9ac122c11a12465c2acbec040) and should have an `@since`

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Commit messages:
 - add an `@since` and modify Copyright header

Changes: https://git.openjdk.org/jdk/pull/19190/files
  Webrev: https://webrevs.openjdk.org/?repo=jdk&pr=19190&range=00
  Issue: https://bugs.openjdk.org/browse/JDK-8332100
  Stats: 3 lines in 1 file changed: 2 ins; 0 del; 1 mod
  Patch: https://git.openjdk.org/jdk/pull/19190.diff
  Fetch: git fetch https://git.openjdk.org/jdk.git pull/19190/head:pull/19190

PR: https://git.openjdk.org/jdk/pull/19190