RFR: 8362598: [macos] Add tests for custom info plist files [v2]

[Alexander Matveev]

> - Added test for custom info plist to cover app image including embedded runtime and runtime installer.
> - Fixed bug in `writePList`. It was missing `writeStartDocument()/writeEndDocument()` and `DOCTYPE` should be full xml string.

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

  8362598: [macos] Add tests for custom info plist files [v3]

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Changes:
  - all: https://git.openjdk.org/jdk/pull/27509/files
  - new: https://git.openjdk.org/jdk/pull/27509/files/50011dad..f1e99130

Webrevs:
 - full: https://webrevs.openjdk.org/?repo=jdk&pr=27509&range=01
 - incr: https://webrevs.openjdk.org/?repo=jdk&pr=27509&range=00-01

  Stats: 212 lines in 6 files changed: 117 ins; 52 del; 43 mod
  Patch: https://git.openjdk.org/jdk/pull/27509.diff
  Fetch: git fetch https://git.openjdk.org/jdk.git pull/27509/head:pull/27509

PR: https://git.openjdk.org/jdk/pull/27509