RFR: 8304818: Prune HttpURLConnection cache when corresponding Authenticator is garbage collected [v7]

[Michael McMahon]

> Hi,
> 
> Can I get a review for this please? This change uses a Cleaner to check when java.net.Authenticator instances become unreachable, and then prunes the authentication cache for entries that correspond to that Authenticator and therefore cannot be used again. This stops the authentication cache from growing in size unbounded. Note, this only happens in the probably unusual case where more than one Authenticator object is used. Normally there is no reason to use more than one instance.
> 
> Thanks,
> Michael.

Michael McMahon 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 ten additional commits since the last revision:

 - Merge branch 'master' into auth
 - removed AuthenticationInfo serialization code plus other updates
 - update
 - Merge branch 'master' into auth
 - updated implementation and reimpl of AuthenticatoKeys
 - review updates
 - test update
 - revert removed methods (used in tests)
 - initial impl

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

Changes:
  - all: https://git.openjdk.org/jdk/pull/13159/files
  - new: https://git.openjdk.org/jdk/pull/13159/files/3c8600f9..6636ac3f

Webrevs:
 - full: https://webrevs.openjdk.org/?repo=jdk&pr=13159&range=06
 - incr: https://webrevs.openjdk.org/?repo=jdk&pr=13159&range=05-06

  Stats: 28635 lines in 725 files changed: 13299 ins; 13590 del; 1746 mod
  Patch: https://git.openjdk.org/jdk/pull/13159.diff
  Fetch: git fetch https://git.openjdk.org/jdk.git pull/13159/head:pull/13159

PR: https://git.openjdk.org/jdk/pull/13159