RFR: 8301004: httpclient: Add more debug to HttpResponseInputStream [v2]

[Daniel Fuchs]

> The AsyncExecutorShutdown test has been observed failing (rarely) in our CI. The root cause seems to be an assertion error in HttpResponseInputStream. More debug traces could help with diagnosing how we reached this assertion.

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

 - Update src/java.net.http/share/classes/jdk/internal/net/http/ResponseSubscribers.java
 - Update src/java.net.http/share/classes/jdk/internal/net/http/ResponseSubscribers.java

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Changes:
  - all: https://git.openjdk.org/jdk/pull/12169/files
  - new: https://git.openjdk.org/jdk/pull/12169/files/885ae064..4387b1ab

Webrevs:
 - full: https://webrevs.openjdk.org/?repo=jdk&pr=12169&range=01
 - incr: https://webrevs.openjdk.org/?repo=jdk&pr=12169&range=00-01

  Stats: 1 line in 1 file changed: 0 ins; 0 del; 1 mod
  Patch: https://git.openjdk.org/jdk/pull/12169.diff
  Fetch: git fetch https://git.openjdk.org/jdk pull/12169/head:pull/12169

PR: https://git.openjdk.org/jdk/pull/12169