[jdk25u] RFR: 8304811: vmTestbase/vm/mlvm/indy/func/jvmti/stepBreakPopReturn/INDIFY_Test.java fails with JVMTI_ERROR_TYPE_MISMATCH

[KavyaKS94]

Clean backport.
SingleStep handler has no checks for thread or location. So once SingleStep event is enabled, event from other thread can be posted first (or several events from different threads).
The fix enables SingleStep event only for test thread. 
Tested changes locally.

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Commit messages:
 - 8304811: vmTestbase/vm/mlvm/indy/func/jvmti/stepBreakPopReturn/INDIFY_Test.java fails with JVMTI_ERROR_TYPE_MISMATCH

Changes: https://git.openjdk.org/jdk25u/pull/286/files
  Webrev: https://webrevs.openjdk.org/?repo=jdk25u&pr=286&range=00
  Issue: https://bugs.openjdk.org/browse/JDK-8304811
  Stats: 3 lines in 1 file changed: 0 ins; 0 del; 3 mod
  Patch: https://git.openjdk.org/jdk25u/pull/286.diff
  Fetch: git fetch https://git.openjdk.org/jdk25u.git pull/286/head:pull/286

PR: https://git.openjdk.org/jdk25u/pull/286