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/Singleton.java

@@ -0,0 +1,21 @@
+package test;
+
+public final class Singleton {
+
+    private Singleton() {}
+
+    private static Singleton INSTANCE;
+
+    public static String getString() {
+        return getInstance().toString();
+    }
+
+    public static Singleton getInstance() {
+        if (INSTANCE == null) {
+            INSTANCE = new Singleton();
+	}
+
+        return INSTANCE;
+    }
+
+}