RFR: JDK-8283416: Update java.lang.invoke.MethodHandle to use sealed classes [v2]

[Joe Darcy]

> Small refactoring to use sealed classes in the MethodHandle implementation hierarchy.
> 
> DelegatingMethodHandle is non-sealed rather than sealed since it has two subclasses, one defined as a nested class and only a separate type in the same package. The permits clause does not allow listed those two kinds of subclasses.
> 
> Please also review the corresponding CSR https://bugs.openjdk.java.net/browse/JDK-8283434

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 three additional commits since the last revision:

 - Respond to review feedback.
 - Merge branch 'master' into JDK-8283416
 - JDK-8283416: Update java.lang.invoke.MethodHandle to use sealed classes

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

Changes:
  - all: https://git.openjdk.java.net/jdk/pull/7881/files
  - new: https://git.openjdk.java.net/jdk/pull/7881/files/f4f79411..e7c6495f

Webrevs:
 - full: https://webrevs.openjdk.java.net/?repo=jdk&pr=7881&range=01
 - incr: https://webrevs.openjdk.java.net/?repo=jdk&pr=7881&range=00-01

  Stats: 65233 lines in 1034 files changed: 62326 ins; 1345 del; 1562 mod
  Patch: https://git.openjdk.java.net/jdk/pull/7881.diff
  Fetch: git fetch https://git.openjdk.java.net/jdk pull/7881/head:pull/7881

PR: https://git.openjdk.java.net/jdk/pull/7881