RFR: 8342566: Improve javadoc of java.lang.annotation.ElementType

[Kevin Bourrillion]

8342566: Improve javadoc of java.lang.annotation.ElementType

-------------

Commit messages:
 - Merge branch 'openjdk:master' into element-type-javadoc
 - Merge branch 'openjdk:master' into element-type-javadoc
 - handle review comments from Chen
 - maybe ready for review now
 - Merge branch 'openjdk:master' into element-type-javadoc
 - keep revising
 - massive rewrite

Changes: https://git.openjdk.org/jdk/pull/21506/files
  Webrev: https://webrevs.openjdk.org/?repo=jdk&pr=21506&range=00
  Issue: https://bugs.openjdk.org/browse/JDK-8342566
  Stats: 164 lines in 1 file changed: 113 ins; 5 del; 46 mod
  Patch: https://git.openjdk.org/jdk/pull/21506.diff
  Fetch: git fetch https://git.openjdk.org/jdk.git pull/21506/head:pull/21506

PR: https://git.openjdk.org/jdk/pull/21506