RFR: 8283660: Convert com/sun/jndi/ldap/AbstractLdapNamingEnumeration.java finalizer to Cleaner [v10]

[Brent Christian]

> Please review this change to replace the finalizer in `AbstractLdapNamingEnumeration` with a Cleaner.
> 
> The pieces of state required for cleanup (`LdapCtx homeCtx`, `LdapResult res`, and `LdapClient enumClnt`) are moved to a static inner class . From there, the change is fairly mechanical.
> 
> Details of note: 
> 1. Some operations need to change the state values (the update() method is probably the most interesting).
> 2. Subclasses need to access `homeCtx`; I added a `homeCtx()` method to read `homeCtx` from the superclass's `state`.
> 
> The test case is based on a copy of `com/sun/jndi/ldap/blits/AddTests/AddNewEntry.java`. A more minimal test case might be possible, but this was done for expediency.
> 
> The test only confirms that the new Cleaner use does not keep the object reachable. It only tests `LdapSearchEnumeration` (not `LdapNamingEnumeration` or `LdapBindingEnumeration`, though all are subclasses of `AbstractLdapNamingEnumeration`). 
> 
> Thanks.

Brent Christian has updated the pull request incrementally with two additional commits since the last revision:

 - added getters to EnumCtx, and moved it to top level ; use getters + local variables to reduce code changes
 - test comment udpate

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

Changes:
  - all: https://git.openjdk.java.net/jdk/pull/8311/files
  - new: https://git.openjdk.java.net/jdk/pull/8311/files/3941e6f1..e34e888f

Webrevs:
 - full: https://webrevs.openjdk.java.net/?repo=jdk&pr=8311&range=09
 - incr: https://webrevs.openjdk.java.net/?repo=jdk&pr=8311&range=08-09

  Stats: 125 lines in 5 files changed: 50 ins; 36 del; 39 mod
  Patch: https://git.openjdk.java.net/jdk/pull/8311.diff
  Fetch: git fetch https://git.openjdk.java.net/jdk pull/8311/head:pull/8311

PR: https://git.openjdk.java.net/jdk/pull/8311