[FE Test] Rename nested directory in testdata into nestedClasses

This is needed to avoid clash between generated test class `Nested` and
  `@Nested` annotation from JUnit 5

compiler/testData/loadJava/compiledKotlin/nestedClasses/innerClassReferencesOuterTP.txt

@@ -0,0 +1,9 @@
+package test
+
+public final class InnerClassReferencesOuterTP</*0*/ P> {
+    /*primary*/ public constructor InnerClassReferencesOuterTP</*0*/ P>()
+
+    public final inner class Inner</*0*/ Q : P> /*captured type parameters: /*1*/ P*/ {
+        /*primary*/ public constructor Inner</*0*/ Q : P>()
+    }
+}