RFR: 8343220: Add test cases to AppContentTest jpackage test [v3]

[Alexey Semenyuk]

> - Update AppContentTest by adding new test cases as requested in the CR.
> - Fix uncovered issue in jpackage: if the same path in the app image is sourced from a file and a directory values of `--app-content` option, it bails out trying to replace the file with the directory and vice versa.

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

  AppContentTest: make it not fail updated IconTest from JDK-8370100.

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Changes:
  - all: https://git.openjdk.org/jdk/pull/27948/files
  - new: https://git.openjdk.org/jdk/pull/27948/files/5b118e5f..81c247e4

Webrevs:
 - full: https://webrevs.openjdk.org/?repo=jdk&pr=27948&range=02
 - incr: https://webrevs.openjdk.org/?repo=jdk&pr=27948&range=01-02

  Stats: 30 lines in 1 file changed: 19 ins; 0 del; 11 mod
  Patch: https://git.openjdk.org/jdk/pull/27948.diff
  Fetch: git fetch https://git.openjdk.org/jdk.git pull/27948/head:pull/27948

PR: https://git.openjdk.org/jdk/pull/27948