RFR: 8302845: Replace finalizer usage in JNDI DNS provider with Cleaner [v2]

[Aleksei Efimov]

> JNDI `DnsClient` has a finalize method to close its internal datagram channel selector.
>  The change proposed here replaces it with a cleaner to close the selector once the `DnsClient`
>   instance becomes phantom reachable. 
> 
> The change was tested with `jdk-tier1` to `jdk-tier3` test sets which showed no failures.

Aleksei Efimov has updated the pull request incrementally with one additional commit since the last revision:

  fix comment

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

Changes:
  - all: https://git.openjdk.org/jdk/pull/13837/files
  - new: https://git.openjdk.org/jdk/pull/13837/files/01840ad9..757d242c

Webrevs:
 - full: https://webrevs.openjdk.org/?repo=jdk&pr=13837&range=01
 - incr: https://webrevs.openjdk.org/?repo=jdk&pr=13837&range=00-01

  Stats: 2 lines in 1 file changed: 0 ins; 0 del; 2 mod
  Patch: https://git.openjdk.org/jdk/pull/13837.diff
  Fetch: git fetch https://git.openjdk.org/jdk.git pull/13837/head:pull/13837

PR: https://git.openjdk.org/jdk/pull/13837