RFR: 8304818: Prune HttpURLConnection cache when corresponding Authenticator is garbage collected [v3]

[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 incrementally with one additional commit since the last revision:

  review updates

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

Changes:
  - all: https://git.openjdk.org/jdk/pull/13159/files
  - new: https://git.openjdk.org/jdk/pull/13159/files/0d435f5a..91a9e4c7

Webrevs:
 - full: https://webrevs.openjdk.org/?repo=jdk&pr=13159&range=02
 - incr: https://webrevs.openjdk.org/?repo=jdk&pr=13159&range=01-02

  Stats: 7 lines in 1 file changed: 2 ins; 0 del; 5 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