RFR: 8376031: HttpsURLConnection.getServerCertificates() throws "java.lang.IllegalStateException: connection not yet open" for the HEAD method [v3]

[Daniel Fuchs]

> The issue here is that `HttpURLConnection` is automatically disconnected (`HttpClient` is set to `null`, `connected` is set to `false`) when a response with no response body bytes is received. This happens before a fake empty body input stream is returned to the user. That behaviour also occurs with any method for which `content-length: 0` is returned (GET, POST, custom, anything), and with any status code (204, 304) for which there is no body.
> 
> In this case, the proposed fix is to store the `SSLSession` in the `AbstractDelegateHttpsURLConnection` subclass until such a time where `disconnect()` is explicitely closed. Information pertaining to SSL, such as server certificates, can be extracted from the saved `SSLSession`.

Daniel Fuchs 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 four additional commits since the last revision:

 - Review feedback: improve the test to verify that certificates are returned
 - Merge branch 'master' into https_certs_8376031
 - Review feedback
 - 8376031: HttpsURLConnection.getServerCertificates() throws "java.lang.IllegalStateException: connection not yet open" for the HEAD method

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Changes:
  - all: https://git.openjdk.org/jdk/pull/29489/files
  - new: https://git.openjdk.org/jdk/pull/29489/files/d962cb8e..abc6e1f6

Webrevs:
 - full: https://webrevs.openjdk.org/?repo=jdk&pr=29489&range=02
 - incr: https://webrevs.openjdk.org/?repo=jdk&pr=29489&range=01-02

  Stats: 41296 lines in 502 files changed: 18470 ins; 14721 del; 8105 mod
  Patch: https://git.openjdk.org/jdk/pull/29489.diff
  Fetch: git fetch https://git.openjdk.org/jdk.git pull/29489/head:pull/29489

PR: https://git.openjdk.org/jdk/pull/29489