* Add tasks to generate source jars for java executables
* native source bundles
* source bundles in separate plugin
* Wire up sourceBundle task
* Produce bundles on a per-variant basis (Java fat jar, each native variant)
* Introduce `pklNativeSourceBundle` and `pklJvmSourceBundle` plugins for handling fat jar vs. GraalVM bits
* Download compiled classes list, and exclude Java sources for executable stuff specifically
* Include native sources when appropriate (GraalVM, JDK, zlib, musl, libpkl)
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Co-authored-by: Jen Basch <jbasch@apple.com>