RFR: 8316017: Refactor timeout handler in PassFailJFrame

[Alexey Ivanov]

Refactored timeout handling in PassFailJFrame:

1. Managing the timer and formatting the time left is inside `TimeoutHandler` class.
2. The class handles timer events and updates the label accordingly.

This is implemented on top of #15665.

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Depends on: https://git.openjdk.org/jdk/pull/15665

Commit messages:
 - 8316017: Refactor timeout handler in PassFailJFrame

Changes: https://git.openjdk.org/jdk/pull/15668/files
 Webrev: https://webrevs.openjdk.org/?repo=jdk&pr=15668&range=00
  Issue: https://bugs.openjdk.org/browse/JDK-8316017
  Stats: 88 lines in 1 file changed: 56 ins; 29 del; 3 mod
  Patch: https://git.openjdk.org/jdk/pull/15668.diff
  Fetch: git fetch https://git.openjdk.org/jdk.git pull/15668/head:pull/15668

PR: https://git.openjdk.org/jdk/pull/15668