Add sourceBundle task to download and prepare source bundles (#1902)

* 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>

pkl-codegen-java/pkl-codegen-java.gradle.kts

@@ -30,6 +30,13 @@ dependencies {
 
   testImplementation(projects.pklConfigJava)
   testImplementation(projects.pklCommonsTest)
+
+  // used by `pklJavaExecutable` plugin (ideally this would be inferred automatically)
+  firstPartySourcesJars(project(":pkl-codegen-java", "sourcesJar"))
+  firstPartySourcesJars(project(":pkl-commons", "sourcesJar"))
+  firstPartySourcesJars(project(":pkl-commons-cli", "sourcesJar"))
+  firstPartySourcesJars(project(":pkl-core", "sourcesJar"))
+  firstPartySourcesJars(project(":pkl-parser", "sourcesJar"))
 }
 
 executable {