RFR: JDK-8267204: Expose access to underlying streams in Reporter [v2]

[Jonathan Gibbons]

> Please review an update to `jdk.javadoc/jdk.javadoc.doclets.Reporter` to add 3 new methods and to improve the descriptions of other parts of the interface.
> 
> The new methods provide access to the underlying streams (informally, for standard output and diagnostic output), and a new `report` method to report diagnostics at an arbitrary position in a file being read by a doclet, or a taglet within a doclet.

Jonathan Gibbons has updated the pull request with a new target base due to a merge or a rebase. The pull request now contains 17 commits:

 - Update copyright years
 - Merge remote-tracking branch 'upstream/master' into jdk-8267204-reporter
 - Merge remote-tracking branch 'upstream/master' into jdk-8267204-reporter
 - Fix typos
 - Fix typos
 - Fix typos
 - Merge remote-tracking branch 'upstream/master' into jdk-8267204-reporter
 - Address review feedback
 - Address review feedback
 - extend Messages to provide convenient access to the new Reporter.report method
 - ... and 7 more: https://git.openjdk.java.net/jdk/compare/20b63127...78e811b1

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Changes: https://git.openjdk.java.net/jdk/pull/4216/files
 Webrev: https://webrevs.openjdk.java.net/?repo=jdk&pr=4216&range=01
  Stats: 545 lines in 10 files changed: 427 ins; 35 del; 83 mod
  Patch: https://git.openjdk.java.net/jdk/pull/4216.diff
  Fetch: git fetch https://git.openjdk.java.net/jdk pull/4216/head:pull/4216

PR: https://git.openjdk.java.net/jdk/pull/4216