RFR: 8258810: Improve enum traits [v3]

[Kim Barrett]

> Please review these miscellaneous improvements to the enum iteration facility.
> Thanks to @albertnetymk for discussions.
> 
> (1) Removed some unneeded stuff from EnumIterationTraits.
> 
> (2) Various similar bits of error checking code are unified and shared via
> EnumIterationTraits.
> 
> (3) Casts between the enum type and the underlying type are now done using
> helper functions in EnumIterationTraits.
> 
> (4) JDK-8257466 added accessors for the EnumRange bounds and the index for
> an enumerator, but didn't account for the possibility of an empty subrange.
> Add assertions for that case.
> 
> (5) Added some death tests to verify some of the error checking.
> 
> Testing:
> mach5 tier1

Kim Barrett 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:

 - Merge branch 'master' into improve_enum_traits
 - update copyrights
 - ayang review
 - Improve enum traits and tests

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

Changes:
  - all: https://git.openjdk.java.net/jdk/pull/1868/files
  - new: https://git.openjdk.java.net/jdk/pull/1868/files/a4667b70..6fdeda47

Webrevs:
 - full: https://webrevs.openjdk.java.net/?repo=jdk&pr=1868&range=02
 - incr: https://webrevs.openjdk.java.net/?repo=jdk&pr=1868&range=01-02

  Stats: 33536 lines in 1245 files changed: 10927 ins; 10970 del; 11639 mod
  Patch: https://git.openjdk.java.net/jdk/pull/1868.diff
  Fetch: git fetch https://git.openjdk.java.net/jdk pull/1868/head:pull/1868

PR: https://git.openjdk.java.net/jdk/pull/1868