RFR: JDK-8151531: Add notes to BaseStream.spliterator/iterator docs regarding them being escape hatches [v3]

[Viktor Klang]

> Still relevant to address? /cc @PaulSandoz

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

  Updating copyright year

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Changes:
  - all: https://git.openjdk.org/jdk/pull/13890/files
  - new: https://git.openjdk.org/jdk/pull/13890/files/4739a781..3f1cb743

Webrevs:
 - full: https://webrevs.openjdk.org/?repo=jdk&pr=13890&range=02
 - incr: https://webrevs.openjdk.org/?repo=jdk&pr=13890&range=01-02

  Stats: 1 line in 1 file changed: 0 ins; 0 del; 1 mod
  Patch: https://git.openjdk.org/jdk/pull/13890.diff
  Fetch: git fetch https://git.openjdk.org/jdk.git pull/13890/head:pull/13890

PR: https://git.openjdk.org/jdk/pull/13890