RFR: JDK-8280534: Enable compile-time doclint reference checking [v3]

[Joe Darcy]

> The changes in this PR on top of the out-for-review changes in https://git.openjdk.java.net/jdk/pull/7222 allow compile-time doclint checking to be enabled in all JDK modules.
> 
> Typically, a @SuppressWarnings("doclint:refernce") annotation is added to declaration with javadoc blocks that have already had distinguished cross-module links added (JDK-8280492).
> 
> One exception is in src/java.base/share/classes/java/net/package-info.java where the cross-module link was (for now) removed. Currently the SuppressWarnings annotation type is not declared to allow its annotations to be applied to package declarations. I'll look into amending that, but in the mean time, I think it is beneficial for the JDK build, and the base module in particular, to have compile-time doclint protections turned on.

Joe Darcy has updated the pull request with a new target base due to a merge or a rebase. The incremental webrev excludes the unrelated changes brought in by the merge/rebase. The pull request contains five additional commits since the last revision:

 - Merge branch 'master' into JDK-8280534
 - Use capabilities of JDK-8280744.
 - Merge branch 'master' into JDK-8280534
 - Cover java.base.
 - JDK-8280534: Enable compile-time doclint reference checking

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

Changes:
  - all: https://git.openjdk.java.net/jdk/pull/7237/files
  - new: https://git.openjdk.java.net/jdk/pull/7237/files/d03401c6..a0b37495

Webrevs:
 - full: https://webrevs.openjdk.java.net/?repo=jdk&pr=7237&range=02
 - incr: https://webrevs.openjdk.java.net/?repo=jdk&pr=7237&range=01-02

  Stats: 1473 lines in 53 files changed: 585 ins; 557 del; 331 mod
  Patch: https://git.openjdk.java.net/jdk/pull/7237.diff
  Fetch: git fetch https://git.openjdk.java.net/jdk pull/7237/head:pull/7237

PR: https://git.openjdk.java.net/jdk/pull/7237