RFR: 8252374: Add a new factory method to concatenate a sequence of BodyPublisher instances into a single publisher. [v8]

[Daniel Fuchs]

> Continuing the review with a PR...
> 
> 8252374: Add a new factory method to concatenate a sequence
>          of BodyPublisher instances into a single publisher.
> https://bugs.openjdk.java.net/browse/JDK-8252374
> 
> 
> Draft CSR:
> https://bugs.openjdk.java.net/browse/JDK-8252382

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 10 additional commits since
the last revision:

 - Merge
 - Added a test case for requesting a non positive number of items.
 - Merge
 - Incorporated review comments
 - Improved the API documentation of BodyPublishers::concat
 - Improved API documentation, added more tests for contentLength()
 - Merge remote-tracking branch 'origin/master' into concat-bs-8252374
 - Merge remote-tracking branch 'origin/master' into concat-bs-8252374
 - Merge remote-tracking branch 'origin/master' into concat-bs-8252374
 - 8252374: Add a new factory method to concatenate a sequence of BodyPublisher instances into a single publisher.

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

Changes:
  - all: https://git.openjdk.java.net/jdk/pull/57/files
  - new: https://git.openjdk.java.net/jdk/pull/57/files/63709bb2..2346c69d

Webrevs:
 - full: https://webrevs.openjdk.java.net/?repo=jdk&pr=57&range=07
 - incr: https://webrevs.openjdk.java.net/?repo=jdk&pr=57&range=06-07

  Stats: 129 lines in 9 files changed: 121 ins; 0 del; 8 mod
  Patch: https://git.openjdk.java.net/jdk/pull/57.diff
  Fetch: git fetch https://git.openjdk.java.net/jdk pull/57/head:pull/57

PR: https://git.openjdk.java.net/jdk/pull/57