RFR: 8256828: ostream::print_cr() truncates buffer in copy-through case

[David Holmes]

Clarifies the behaviour of this function in regards to truncation when adding a CR. Ensures a truncation warning is always issued.

Adds unit testing for the specialized cases.

See JBS for discussion of other suggestions.

Testing: - tiers 1-4

Thanks

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Commit messages:
 - Correct comment
 - Merge branch 'master' into 8256828-ostream
 - 8256828: ostream::print_cr() truncates buffer in copy-through case

Changes: https://git.openjdk.org/jdk/pull/19512/files
  Webrev: https://webrevs.openjdk.org/?repo=jdk&pr=19512&range=00
  Issue: https://bugs.openjdk.org/browse/JDK-8256828
  Stats: 315 lines in 4 files changed: 296 ins; 2 del; 17 mod
  Patch: https://git.openjdk.org/jdk/pull/19512.diff
  Fetch: git fetch https://git.openjdk.org/jdk.git pull/19512/head:pull/19512

PR: https://git.openjdk.org/jdk/pull/19512