Desktop: ship the stdlib with a packaged app (jar/jpackage), not only via PYTHONHOME for Gradle tasks #60

The plugin sets PYTHONHOME only on JavaExec/Test tasks; a packaged desktop app gets no stdlib (ROADMAP 15.4). Scope: package the acquired python-build-standalone stdlib with the desktop distribution (jpackage app image / jar resource extracted like the python/ payload) and point PYTHONHOME at it at startup. Ownership as in the iOS issue: python-multiplatform owns interpreter/stdlib; toolchain ships python/ only.

Completion: a packaged sample app (createDistributable) runs a stdlib import with no PYTHONHOME in the environment.