Add included build to JAR

Instead of copying classes to the compile output, we now add them directly to the JAR.
This allows JavaCompile to be cached, since there are no overlapping outputs anymore.

core/spring-security-core.gradle

@@ -34,12 +34,7 @@ dependencies {
 	testRuntime 'org.hsqldb:hsqldb'
 }
 
-classes.doLast {
-	copy {
-		from includeProject.sourceSets.main.output
-		into sourceSets.main.java.outputDir
-	}
-}
+tasks.jar.from { includeProject.sourceSets.main.output }
 
 tasks.sourcesJar.from {includeProject.sourceSets.main.java}