RFR: 8303682: Simplify HttpClient DebugLogger [v2]

[Daniel Fuchs]

> The HttpClient internal DebugLogger could be simplified if its configuration was held in a record. Some of the methods in Utils that return a debug logger could also be simplified/removed. The system property that configures the debug logging could be extended to choose between System.err, System.out, System.Logger, or any of these configurations.
> Passing -Djdk.internal.httpclient.debug=true still works as before.

Daniel Fuchs has updated the pull request incrementally with two additional commits since the last revision:

 - Make sure julLogger is not GC'ed before the end of the test.
 - Integrated review feedback

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Changes:
  - all: https://git.openjdk.org/jdk/pull/12900/files
  - new: https://git.openjdk.org/jdk/pull/12900/files/50388609..6dca758e

Webrevs:
 - full: https://webrevs.openjdk.org/?repo=jdk&pr=12900&range=01
 - incr: https://webrevs.openjdk.org/?repo=jdk&pr=12900&range=00-01

  Stats: 46 lines in 3 files changed: 27 ins; 2 del; 17 mod
  Patch: https://git.openjdk.org/jdk/pull/12900.diff
  Fetch: git fetch https://git.openjdk.org/jdk pull/12900/head:pull/12900

PR: https://git.openjdk.org/jdk/pull/12900