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

[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.

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

Commit messages:
 - 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.

Changes: https://git.openjdk.java.net/jdk/pull/5007/files
 Webrev: https://webrevs.openjdk.java.net/?repo=jdk&pr=5007&range=00
  Issue: https://bugs.openjdk.java.net/browse/JDK-8140442
  Stats: 322 lines in 6 files changed: 268 ins; 53 del; 1 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