Introduce experimental -Xuse-javac compilation mode

In this mode, javac AST and Symbol files are used during
Kotlin compilation instead of PSI / binary stuff.
Later, they are reused for Java file compilation.
javac in this mode is integrated into kotlinc.

compiler/testData/compileKotlinAgainstJava/SeveralInnerClasses.java

@@ -0,0 +1,19 @@
+package test;
+
+public class SeveralInnerClasses {
+
+    public static class NestedFirst {
+        public static class NestedSecond {
+        }
+    }
+
+    public class InnerFirst {
+        public class InnerSecond {
+        }
+    }
+
+    public static NestedFirst.NestedSecond getNested() { return null; }
+
+    public static InnerFirst.InnerSecond getInner() { return null; }
+
+}