RFR: JDK-8282411: Add useful predicates to ElementKind [v2]

[Joe Darcy]

> Discussion from a recent review in javadoc, adding some more functionality to ElementKind predicates.
> 
> Please also review the CSR: https://bugs.openjdk.java.net/browse/JDK-8282461

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 four additional commits since the last revision:

 - Improve whitespace.
 - Merge branch 'master' into JDK-8282411
 - Add tests.
 - JDK-8282411: Add useful predicates to ElementKind

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

Changes:
  - all: https://git.openjdk.java.net/jdk/pull/7637/files
  - new: https://git.openjdk.java.net/jdk/pull/7637/files/7d423d65..c72518b5

Webrevs:
 - full: https://webrevs.openjdk.java.net/?repo=jdk&pr=7637&range=01
 - incr: https://webrevs.openjdk.java.net/?repo=jdk&pr=7637&range=00-01

  Stats: 7179 lines in 217 files changed: 4818 ins; 1227 del; 1134 mod
  Patch: https://git.openjdk.java.net/jdk/pull/7637.diff
  Fetch: git fetch https://git.openjdk.java.net/jdk pull/7637/head:pull/7637

PR: https://git.openjdk.java.net/jdk/pull/7637