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/ReturnNested.java

@@ -0,0 +1,11 @@
+package test;
+
+public class ReturnNested {
+
+    public static class Nested {
+        
+    }
+
+    public Nested getNested() { return new Nested(); }
+
+}