RFR: 8224243: Make AccessibleObject a sealed class [v3]

[Joe Darcy]

> Conceptually, AccessbileObject is a sealed class with a protected constructor stating
> 
>     Constructor: only used by the Java Virtual Machine.
> 
> With the language now supporting sealed classes, the AccessbileObject should be marked as sealed.
> 
> Executable and Field are the subclasses of AccessbileObject in the JDK; as Executable has subclasses, it is marked as non-sealed.
> 
> Please also review the corresponding CSR:
> 
> https://bugs.openjdk.java.net/browse/JDK-8224243

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 five additional commits since the last revision:

 - Minor fixes.
 - Change to UnsupportedOperationException.
 - Merge branch 'master' into 8224243
 - Update in response to review feedback.
 - 8224243: Make AccessibleObject a sealed class

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

Changes:
  - all: https://git.openjdk.java.net/jdk/pull/4133/files
  - new: https://git.openjdk.java.net/jdk/pull/4133/files/be517cda..8d0ba447

Webrevs:
 - full: https://webrevs.openjdk.java.net/?repo=jdk&pr=4133&range=02
 - incr: https://webrevs.openjdk.java.net/?repo=jdk&pr=4133&range=01-02

  Stats: 5955 lines in 975 files changed: 2860 ins; 1801 del; 1294 mod
  Patch: https://git.openjdk.java.net/jdk/pull/4133.diff
  Fetch: git fetch https://git.openjdk.java.net/jdk pull/4133/head:pull/4133

PR: https://git.openjdk.java.net/jdk/pull/4133