Bundle source in jar (wpilibsuite#589)

This used to be done in Eclipse Plugins, allowing teams that lost their
source to recover it from the jar on the roboRIO.

vscode-wpilib/resources/gradle/java/build.gradle

@@ -84,6 +84,7 @@ wpi.sim.addDriverstation()
 // knows where to look for our Robot Class.
 jar {
     from { configurations.runtimeClasspath.collect { it.isDirectory() ? it : zipTree(it) } }
+    from sourceSets.main.allSource
     manifest edu.wpi.first.gradlerio.GradleRIOPlugin.javaManifest(ROBOT_MAIN_CLASS)
     duplicatesStrategy = DuplicatesStrategy.INCLUDE
 }