RFR: 8310996: Add JFR event for connect operations [v8]

[Tim Prinzing]

> Adds a JFR event for socket connect operations.
> 
> Existing tests TestSocketEvents and TestSocketChannelEvents modified to also check for connect events.

Tim Prinzing has updated the pull request incrementally with one additional commit since the last revision:

  requests fixes
  
  - Use IOException.toString() instead of getMessage() in case it's empty
  - Attempts to test connect exceptions may fail due to unexpected
    successful connect.  Tests quit with uncompleted status if the
    connect is successful and are retried a small number of times until
    the test can be performed properly.  If the retries are exceeded an
    exception is generated indicating the test can't be setup properly.

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

Changes:
  - all: https://git.openjdk.org/jdk/pull/21528/files
  - new: https://git.openjdk.org/jdk/pull/21528/files/a379609e..5e55ffc6

Webrevs:
 - full: https://webrevs.openjdk.org/?repo=jdk&pr=21528&range=07
 - incr: https://webrevs.openjdk.org/?repo=jdk&pr=21528&range=06-07

  Stats: 62 lines in 6 files changed: 43 ins; 3 del; 16 mod
  Patch: https://git.openjdk.org/jdk/pull/21528.diff
  Fetch: git fetch https://git.openjdk.org/jdk.git pull/21528/head:pull/21528

PR: https://git.openjdk.org/jdk/pull/21528