RFR: 8273456: Do not hold ttyLock around stack walking

[Coleen Phillimore]

This change moves the tty rank back down to near access, and prints stack traces to stringStream to avoid holding the tty lock while trying to take the stackwatermark lock.
Tested with tier1-8 (7,8 still in progress but no failures so far).

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Commit messages:
 - 8273456: Do not hold ttyLock around stack walking

Changes: https://git.openjdk.java.net/jdk/pull/5445/files
 Webrev: https://webrevs.openjdk.java.net/?repo=jdk&pr=5445&range=00
  Issue: https://bugs.openjdk.java.net/browse/JDK-8273456
  Stats: 126 lines in 5 files changed: 54 ins; 45 del; 27 mod
  Patch: https://git.openjdk.java.net/jdk/pull/5445.diff
  Fetch: git fetch https://git.openjdk.java.net/jdk pull/5445/head:pull/5445

PR: https://git.openjdk.java.net/jdk/pull/5445