RFR: 8283660: Convert com/sun/jndi/ldap/AbstractLdapNamingEnumeration.java finalizer to Cleaner [v2]

[Brent Christian]

> Please review this change to replace the finalizer in `AbstractLdapNamingEnumeration` with Cleaner.
> 
> (The [first PR](https://github.com/openjdk/jdk/pull/8311) for this fix started some substantial discussions, leading to, among other things, the [8314480](https://bugs.openjdk.org/browse/JDK-8314480) `java.lang.ref` memory ordering spec update.)
> 
> In standard fashion, pieces of state required for cleanup (`LdapCtx homeCtx`, `LdapResult res`, and `LdapClient enumClnt`) are moved into a _Context_ object. 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). Use of `reachabilityFence()` ensures memory visibility on the Cleaner thread (per the aforementioned spec update).
> 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`. It confirms that the use of Cleaner does not keep an `LdapSearchEnumeration` object reachable. The other `AbstractLdapNamingEnumeration` subclasses (`LdapNamingEnumeration` and `LdapBindingEnumeration`) can be expected to behave the same.
> 
> Thanks.
> 
> **Edit: (Re)viewers: due to there being a lot of indentation changes, you might consider enabling the "Hide whitespace" option on the "Files changed" tab. To my eye, it gives a better view of the changes.**

Brent Christian has updated the pull request incrementally with one additional commit since the last revision:

  update copyright

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

Changes:
  - all: https://git.openjdk.org/jdk/pull/25242/files
  - new: https://git.openjdk.org/jdk/pull/25242/files/e36cf5db..c3a94433

Webrevs:
 - full: https://webrevs.openjdk.org/?repo=jdk&pr=25242&range=01
 - incr: https://webrevs.openjdk.org/?repo=jdk&pr=25242&range=00-01

  Stats: 1 line in 1 file changed: 0 ins; 0 del; 1 mod
  Patch: https://git.openjdk.org/jdk/pull/25242.diff
  Fetch: git fetch https://git.openjdk.org/jdk.git pull/25242/head:pull/25242

PR: https://git.openjdk.org/jdk/pull/25242