RFR: 8252713: jtreg time out of CtrlASCII.java seems to hang the Xserver. [v2]

[Alexander Zvegintsev]

> This test needs more stabilization:
> 
> - The test can be easily hang by replacing <br> iteration on `keycharHash.elements()` with `keycharHash.forEach((k, v) -> punchCtrlKey(robot, v));` 
> I do not see any reason why we need a synchronized `Hashtable`, so switched to `HashMap`
> Looks like it might be a reason of original test hanging.
> - `keyRelease`, `dispose` calls wrapped with finally block
> - Just to be safe added timeout `@run main/timeout=600` ( none of the CI test runs took too long thought)
> 
> CI testing looks good on all platforms.

Alexander Zvegintsev has updated the pull request incrementally with one additional commit since the last revision:

  formatting clean up

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

Changes:
  - all: https://git.openjdk.org/jdk/pull/11214/files
  - new: https://git.openjdk.org/jdk/pull/11214/files/e53dcead..102ff6c3

Webrevs:
 - full: https://webrevs.openjdk.org/?repo=jdk&pr=11214&range=01
 - incr: https://webrevs.openjdk.org/?repo=jdk&pr=11214&range=00-01

  Stats: 20 lines in 1 file changed: 0 ins; 2 del; 18 mod
  Patch: https://git.openjdk.org/jdk/pull/11214.diff
  Fetch: git fetch https://git.openjdk.org/jdk pull/11214/head:pull/11214

PR: https://git.openjdk.org/jdk/pull/11214