RFR: 8371076: jpackage will wrongly overwrite the plist file in the embedded runtime when executed with the "--app-image" option [v2]

[Alexey Semenyuk]

> - Fix MacPackagingPipeline.
> - Fix AppImageSigner: this is the follow-up for MacPackagingPipeline fix. Without fixing AppImageSigner AppImagePackageTest.testEmpty test fails. It happened that the test passed because jpackage wrongly created the plist file for the embedded runtime in the case of the predefined app image. The test passed because of the bug in jpackage fixed in this PR.
> - Add test cases for predefined app image packaging to the CustomInfoPListTest test. They had been failing before MacPackagingPipeline was fixed.
> 
> Supplementary changes:
>  - Get rid of duplicated `createInputRuntimeImage()` and `createRuntimeBundle()` functions.
>  - Improve `MacHelper.writeFaPListFragment()` to work with a predefined app image.
>  - Add optional tracing to the packaging pipeline (turned off by default, must edit static fields to enable in custom builds).
>  - PListReader: add find methods that return an Optional instead of throwing an exception when the requested key is not found; update unit tests.

Alexey Semenyuk has updated the pull request incrementally with two additional commits since the last revision:

 - CustomInfoPListTest: use Slot class
 - Add Slot utility class

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

Changes:
  - all: https://git.openjdk.org/jdk/pull/28089/files
  - new: https://git.openjdk.org/jdk/pull/28089/files/746a2220..494adc56

Webrevs:
 - full: https://webrevs.openjdk.org/?repo=jdk&pr=28089&range=01
 - incr: https://webrevs.openjdk.org/?repo=jdk&pr=28089&range=00-01

  Stats: 59 lines in 2 files changed: 47 ins; 0 del; 12 mod
  Patch: https://git.openjdk.org/jdk/pull/28089.diff
  Fetch: git fetch https://git.openjdk.org/jdk.git pull/28089/head:pull/28089

PR: https://git.openjdk.org/jdk/pull/28089