RFR: 8257466: Improve enum iteration [v2]

[Kim Barrett]

> Please review this collection of improvements to the recently added enum
> iteration facility. These improvements are based on usage in some
> in-development changes.
> 
> (1) Added EnumType nested type to EnumRange and EnumIterator. It is an alias
> for the enum type that is a template parameter for those classes. This is
> useful when dealing with a range or iterator whose associated enum type is
> not known because the range/iterator is a template parameter.
> 
> (2) Added EnumRange<T>::index(T), which converts the argument enumerator to
> a zero-based index into the range of values. This is useful when mapping
> from an enumerator to a corresponding array index, for example.
> 
> (3) Allow enum range bounds to be specified using start and (exclusive) end
> integral (underlying type) values. This is useful when dealing with enums
> that are just value ranges and don't have named enumerators. As part of
> this, changes the enum iteration traits mechanism to use start/end rather
> than first/last, as that seems to be a little easier to deal with.
> 
> (4) Added accessors for the first and last enumerator values of a range.
> 
> (5) Added gtest for enum iteration.
> 
> Testing: tier1

Kim Barrett has updated the pull request incrementally with one additional commit since the last revision:

  iklam review

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

Changes:
  - all: https://git.openjdk.java.net/jdk/pull/1530/files
  - new: https://git.openjdk.java.net/jdk/pull/1530/files/3a4dbd5c..6911c0fa

Webrevs:
 - full: https://webrevs.openjdk.java.net/?repo=jdk&pr=1530&range=01
 - incr: https://webrevs.openjdk.java.net/?repo=jdk&pr=1530&range=00-01

  Stats: 9 lines in 1 file changed: 0 ins; 7 del; 2 mod
  Patch: https://git.openjdk.java.net/jdk/pull/1530.diff
  Fetch: git fetch https://git.openjdk.java.net/jdk pull/1530/head:pull/1530

PR: https://git.openjdk.java.net/jdk/pull/1530