[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/deepInnerGeneric.kt

@@ -0,0 +1,13 @@
+package test
+
+class A<TA> {
+    inner class B<TB> {
+        inner class C<TC> {
+            inner class D<TD> {
+                fun <P1, P2, P3, P4> foo(p1: P1, p2: P2, p3: P3, p4: P4): Nothing = null!!
+
+                fun bar(ta: TA, tb: TB, tc: TC, td: TD): A<TA>.B<TB>.C<TC>.D<TD> = foo<TA, TB, TC, TD>(ta, tb, tc, td)
+            }
+        }
+    }
+}