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/UseKotlinInner.java

@@ -0,0 +1,16 @@
+package test;
+
+public class UseKotlinInner extends KotlinClass {
+
+    KotlinInner getKotlinInner() { return null; }
+
+    JavaInner getJavaInner() { return null; }
+
+    KotlinInner3 getKotlinInner3() { return null; }
+}
+
+class JavaClass2  {
+
+    static class JavaInner {}
+
+}