RFR: 8267832: SimpleVisitors and Scanners in jdk.compiler should use @implSpec

[Jan Lahoda]

As noted in:
https://bugs.openjdk.java.net/browse/JDK-8265981?focusedCommentId=14423316&page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel#comment-14423316

Methods in various utility visitor classes in jdk.compiler should use @implSpec to specify the implementation behavior. This patch tries to add the @implSpec tag to methods which already contain a text specifying the implementation, and adds new javadoc to the handful of methods that are missing it so far.

The CSR is started for review here:
https://bugs.openjdk.java.net/browse/JDK-8267838

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Depends on: https://git.openjdk.java.net/jdk/pull/3863

Commit messages:
 - 8267832: SimpleVisitors and Scanners in jdk.compiler should use @implSpec

Changes: https://git.openjdk.java.net/jdk/pull/4223/files
 Webrev: https://webrevs.openjdk.java.net/?repo=jdk&pr=4223&range=00
  Issue: https://bugs.openjdk.java.net/browse/JDK-8267832
  Stats: 692 lines in 4 files changed: 500 ins; 0 del; 192 mod
  Patch: https://git.openjdk.java.net/jdk/pull/4223.diff
  Fetch: git fetch https://git.openjdk.java.net/jdk pull/4223/head:pull/4223

PR: https://git.openjdk.java.net/jdk/pull/4223