RFR: 8279361: Error in documentation of third Stream.reduce method [v3]

[Viktor Klang]

> This JavaDoc change attempts to shine some light on the `combiner`-function as it relates to the third variant of `Stream.reduce` since it according to the bug submission in JBS can be confusing that the `combiner` is not mentioned in the code example in the documentation.

Viktor Klang has updated the pull request incrementally with one additional commit since the last revision:

  Updating the copyright year to 2022 for changes related to issue 8279361

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Changes:
  - all: https://git.openjdk.org/jdk/pull/10469/files
  - new: https://git.openjdk.org/jdk/pull/10469/files/5f93e779..83706e0c

Webrevs:
 - full: https://webrevs.openjdk.org/?repo=jdk&pr=10469&range=02
 - incr: https://webrevs.openjdk.org/?repo=jdk&pr=10469&range=01-02

  Stats: 3 lines in 3 files changed: 0 ins; 0 del; 3 mod
  Patch: https://git.openjdk.org/jdk/pull/10469.diff
  Fetch: git fetch https://git.openjdk.org/jdk pull/10469/head:pull/10469

PR: https://git.openjdk.org/jdk/pull/10469