Build maven-like stdlib sources artifacts during dist

This is needed to emulate gradle and maven like projects in plugin tests.

libraries/stdlib/common/build.gradle

@@ -120,6 +120,7 @@ artifacts {
 // TODO: call the "dist" task instead, once we need to publish kotlin-stdlib-common.jar with the compiler distribution
 task distCommon(type: Copy) {
     from(jar)
+    from(sourcesJar)
     into "$distDir/common"
     rename "-${java.util.regex.Pattern.quote(version)}", ''
 }