RFR: 8140442: Add getOutermostTypeElement to javax.lang.model utility class [v3]

[Joe Darcy]

> Please review this change to add a getOutermostTypeElement method to javax.lang.model.Elements along with the corresponding CSR https://bugs.openjdk.java.net/browse/JDK-8271903.

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 seven additional commits since the last revision:

 - Merge branch 'master' into JDK-8140442
 - Respond to review feedback and update copyright.
 - Appease jcheck.
 - Now with tests and javac Elements implementation.
 - Merge branch 'master' into JDK-8140442
 - Merge branch 'master' into JDK-8140442
 - Initial version pre-tests.

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Changes:
  - all: https://git.openjdk.java.net/jdk/pull/5007/files
  - new: https://git.openjdk.java.net/jdk/pull/5007/files/3ac05554..7f58ab5b

Webrevs:
 - full: https://webrevs.openjdk.java.net/?repo=jdk&pr=5007&range=02
 - incr: https://webrevs.openjdk.java.net/?repo=jdk&pr=5007&range=01-02

  Stats: 6854 lines in 191 files changed: 5916 ins; 432 del; 506 mod
  Patch: https://git.openjdk.java.net/jdk/pull/5007.diff
  Fetch: git fetch https://git.openjdk.java.net/jdk pull/5007/head:pull/5007

PR: https://git.openjdk.java.net/jdk/pull/5007