Align generic signature for inner classes to work as in Java

#KT-10397 Fixed

According to JVMS (p. 4.3.4) inner classes should be separated with `$` in generic signature.

Note that in Java, inner types separated with `.` after first parameterized type, and now we preserve the same behaviour. See tests for clarification.

compiler/testData/codegen/box/reflection/genericSignature/signatureOfSimpleInnerSimpleOuter.kt

@@ -0,0 +1,15 @@
+// WITH_REFLECT
+// IGNORE_BACKEND: JS, NATIVE
+
+abstract class Outer {
+    inner class Inner
+    fun foo(): Inner? = null
+}
+
+fun box(): String {
+    kotlin.test.assertEquals(
+            "class Outer\$Inner",
+            Outer::class.java.declaredMethods.single().genericReturnType.toString())
+
+    return "OK"
+}