RFR: 8343875: Minor improvements of jpackage test library [v2]

[Alexey Semenyuk]

> The PR affects jpackage test library only. Changes:
> 
> - Removed dependencies on `java.io.File`. `java.io.File.pathSeparator` is still used as there is no better alternative.
> - Use `TKit.concatMessages()` instead of `String.format()` in TKit.assert...() methods.
> - Added unit tests for all TKit.assert...() modified methods.
> - Added unit tests for `JavaAppDesc` class.
> - Added `jdk.jpackage.test.TestSuite` class to automatically run all jpackage test library unit tests. This eliminates the need to add jtreg comments to every jpackage test library unit test java source.

Alexey Semenyuk has updated the pull request incrementally with one additional commit since the last revision:

  Remove redundant space char

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

Changes:
  - all: https://git.openjdk.org/jdk/pull/21995/files
  - new: https://git.openjdk.org/jdk/pull/21995/files/7f76e829..c669b243

Webrevs:
 - full: https://webrevs.openjdk.org/?repo=jdk&pr=21995&range=01
 - incr: https://webrevs.openjdk.org/?repo=jdk&pr=21995&range=00-01

  Stats: 1 line in 1 file changed: 0 ins; 0 del; 1 mod
  Patch: https://git.openjdk.org/jdk/pull/21995.diff
  Fetch: git fetch https://git.openjdk.org/jdk.git pull/21995/head:pull/21995

PR: https://git.openjdk.org/jdk/pull/21995