RFR: JDK-8283230: Improve @jls usage in ElementType

[Joe Darcy]

Improve some semantic links into JLS with actual links.

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Commit messages:
 - JDK-8283230: Improve @jls usage in ElementType

Changes: https://git.openjdk.java.net/jdk/pull/7831/files
 Webrev: https://webrevs.openjdk.java.net/?repo=jdk&pr=7831&range=00
  Issue: https://bugs.openjdk.java.net/browse/JDK-8283230
  Stats: 3 lines in 1 file changed: 0 ins; 0 del; 3 mod
  Patch: https://git.openjdk.java.net/jdk/pull/7831.diff
  Fetch: git fetch https://git.openjdk.java.net/jdk pull/7831/head:pull/7831

PR: https://git.openjdk.java.net/jdk/pull/7831