RFR: 8364819: Cleanup handshake_timed_out_thread and safepoint_timed_out_thread

[Anton Artemov]

Hi, please consider the following changes:

This is a cleanup after https://github.com/openjdk/jdk/pull/26309

1) `_handshake_timed_out_thread `and `_safepoint_timed_out_thread` are now `Thread*` and not `intptr_t`, no conversions `p2i <-> i2p` needed.

2) Added a missed brace in the error message. 

Trivial change.

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Commit messages:
 - 8364819: Cleanup

Changes: https://git.openjdk.org/jdk/pull/26656/files
  Webrev: https://webrevs.openjdk.org/?repo=jdk&pr=26656&range=00
  Issue: https://bugs.openjdk.org/browse/JDK-8364819
  Stats: 16 lines in 4 files changed: 0 ins; 0 del; 16 mod
  Patch: https://git.openjdk.org/jdk/pull/26656.diff
  Fetch: git fetch https://git.openjdk.org/jdk.git pull/26656/head:pull/26656

PR: https://git.openjdk.org/jdk/pull/26656