RFR: 8328402: Implement pausing functionality for the PassFailJFrame [v2]

[Alexander Zvegintsev]

>> we need to add next to Pass/Fail a "Pause Timer" button, that
> (a) stops the count down
> (b) changes the Pause Timer to "Resume Timer"
> ~~(c) disables Pass/Fail until the timer is resumed~~
> the test will not have to pause or be aware - only the PassFailJFrame machinery.
> ~~So the tester can do anything they want except exit the test in the paused mode.~~
> 
> This PR implements everything except the (c).
> I see nothing wrong with completing the test from the paused state, and it does not add an extra click.  
> 
> 
> Example screenshots:
> 
> ![image](https://github.com/openjdk/jdk/assets/77687766/65d34bf8-1e46-4e68-b39e-a77f257ec3c0)
> ![image](https://github.com/openjdk/jdk/assets/77687766/3a43e059-2d48-46f3-9d1b-c2ab84fcce37)

Alexander Zvegintsev has updated the pull request incrementally with two additional commits since the last revision:

 - TimeoutHandler -> TimeoutHandlerPanel
 - review comments

-------------

Changes:
  - all: https://git.openjdk.org/jdk/pull/18368/files
  - new: https://git.openjdk.org/jdk/pull/18368/files/85ba846a..10f4580e

Webrevs:
 - full: https://webrevs.openjdk.org/?repo=jdk&pr=18368&range=01
 - incr: https://webrevs.openjdk.org/?repo=jdk&pr=18368&range=00-01

  Stats: 38 lines in 1 file changed: 15 ins; 9 del; 14 mod
  Patch: https://git.openjdk.org/jdk/pull/18368.diff
  Fetch: git fetch https://git.openjdk.org/jdk.git pull/18368/head:pull/18368

PR: https://git.openjdk.org/jdk/pull/18368