RFR: 8271348: Add stronger sanity check of thread state when polling for safepoint/handshakes

[Daniel D.Daugherty]

A trivial follow-up to:

JDK-8271251 JavaThread::java_suspend() fails with "fatal error: Illegal threadstate encountered: 6"

that adds a stronger sanity check of thread state when polling for safepoint/handshakes.

This fix was used to test @pchilano's fix for JDK-8271251 in my JDK17 Mach5
Tier[1-8] runs for JDK-8271251. It has also been tested with Mach5 Tier[1-3]
for jdk/jdk (JDK18).

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Commit messages:
 - 8271348: Add stronger sanity check of thread state when polling for safepoint/handshakes

Changes: https://git.openjdk.java.net/jdk/pull/4936/files
 Webrev: https://webrevs.openjdk.java.net/?repo=jdk&pr=4936&range=00
  Issue: https://bugs.openjdk.java.net/browse/JDK-8271348
  Stats: 48 lines in 3 files changed: 20 ins; 16 del; 12 mod
  Patch: https://git.openjdk.java.net/jdk/pull/4936.diff
  Fetch: git fetch https://git.openjdk.java.net/jdk pull/4936/head:pull/4936

PR: https://git.openjdk.java.net/jdk/pull/4936