Moved current incremental compiler test data into subdirectory.

Tweaked test generator to avoid creating test methods for parent directory of tests.

jps-plugin/testData/incremental/pureKotlin/classSignatureUnchanged/usage.kt

@@ -0,0 +1,6 @@
+package test
+
+fun usage(a: Klass) {
+    a.foo()
+    a.bar()
+}