RFR: 8306785: fix deficient spliterators for Sequenced Collections

Wed Jul 12 23:24:28 UTC 2023

Change some reverse-ordered spliterators to use `Spliterators.spliterator(Collection, ORDERED)` instead of `Spliterators.spliteratorUnknownSize()`. This gives SIZED and ORDERED spliterators. More optimizations will be done later. I'm intending to backport this to JDK 21 so I want this to be minimal.

I've also included some adjustments to spliterator implementation comments to clear up a few points of confusion. (No spec changes.)

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

Commit messages:
 - Update some Spliterator comments; change default views to use spliterator(Collection).

Changes: https://git.openjdk.org/jdk/pull/14854/files
 Webrev: https://webrevs.openjdk.org/?repo=jdk&pr=14854&range=00
  Issue: https://bugs.openjdk.org/browse/JDK-8306785
  Stats: 30 lines in 6 files changed: 18 ins; 4 del; 8 mod
  Patch: https://git.openjdk.org/jdk/pull/14854.diff
  Fetch: git fetch https://git.openjdk.org/jdk.git pull/14854/head:pull/14854

PR: https://git.openjdk.org/jdk/pull/14854